#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")

struct Hld {
  int n, rt;
  // needs to be tree
  // vertex lists
  // modified in build(rt) (parent removed, heavy child first)
  vector<vector<int>> graph;
  vector<int> sz, par, dep;
  int zeit;
  vector<int> dis, fin, sid;
  // head vertex (minimum depth) in heavy path
  vector<int> head;

  Hld() : n(0), rt(-1), zeit(0) {}
  explicit Hld(int n_) : n(n_), rt(-1), graph(n), zeit(0) {}
  void ae(int u, int v) {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    graph[u].push_back(v);
    graph[v].push_back(u);
  }

  void dfsSz(int u) {
    sz[u] = 1;
    for (const int v : graph[u]) {
      auto it = std::find(graph[v].begin(), graph[v].end(), u);
      if (it != graph[v].end()) graph[v].erase(it);
      par[v] = u;
      dep[v] = dep[u] + 1;
      dfsSz(v);
      sz[u] += sz[v];
    }
  }
  void dfsHld(int u) {
    dis[u] = zeit++;
    const int deg = graph[u].size();
    if (deg > 0) {
      int vm = graph[u][0];
      int jm = 0;
      for (int j = 1; j < deg; ++j) {
        const int v = graph[u][j];
        if (sz[vm] < sz[v]) {
          vm = v;
          jm = j;
        }
      }
      swap(graph[u][0], graph[u][jm]);
      head[vm] = head[u];
      dfsHld(vm);
      for (int j = 1; j < deg; ++j) {
        const int v = graph[u][j];
        head[v] = v;
        dfsHld(v);
      }
    }
    fin[u] = zeit;
  }
  void build(int rt_) {
    assert(0 <= rt_); assert(rt_ < n);
    rt = rt_;
    sz.assign(n, 0);
    par.assign(n, -1);
    dep.assign(n, -1);
    dep[rt] = 0;
    dfsSz(rt);
    zeit = 0;
    dis.assign(n, -1);
    fin.assign(n, -1);
    head.assign(n, -1);
    head[rt] = rt;
    dfsHld(rt);
    assert(zeit == n);
    sid.assign(n, -1);
    for (int u = 0; u < n; ++u) sid[dis[u]] = u;
  }

  friend ostream &operator<<(ostream &os, const Hld &hld) {
    const int maxDep = *max_element(hld.dep.begin(), hld.dep.end());
    vector<string> ss(2 * maxDep + 1);
    int pos = 0, maxPos = 0;
    for (int j = 0; j < hld.n; ++j) {
      const int u = hld.sid[j];
      const int d = hld.dep[u];
      if (hld.head[u] == u) {
        if (j != 0) {
          pos = maxPos + 1;
          ss[2 * d - 1].resize(pos, '-');
          ss[2 * d - 1] += '+';
        }
      } else {
        ss[2 * d - 1].resize(pos, ' ');
        ss[2 * d - 1] += '|';
      }
      ss[2 * d].resize(pos, ' ');
      ss[2 * d] += std::to_string(u);
      if (maxPos < static_cast<int>(ss[2 * d].size())) {
        maxPos = ss[2 * d].size();
      }
    }
    for (int d = 0; d <= 2 * maxDep; ++d) os << ss[d] << '\n';
    return os;
  }

  bool contains(int u, int v) const {
    return (dis[u] <= dis[v] && dis[v] < fin[u]);
  }
  int lca(int u, int v) const {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    for (; head[u] != head[v]; ) (dis[u] > dis[v]) ? (u = par[head[u]]) : (v = par[head[v]]);
    return (dis[u] > dis[v]) ? v : u;
  }
  int jumpUp(int u, int d) const {
    assert(0 <= u); assert(u < n);
    assert(d >= 0);
    if (dep[u] < d) return -1;
    const int tar = dep[u] - d;
    for (u = head[u]; ; u = head[par[u]]) {
      if (dep[u] <= tar) return sid[dis[u] + (tar - dep[u])];
    }
  }
  int jump(int u, int v, int d) const {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    assert(d >= 0);
    const int l = lca(u, v);
    const int du = dep[u] - dep[l], dv = dep[v] - dep[l];
    if (d <= du) {
      return jumpUp(u, d);
    } else if (d <= du + dv) {
      return jumpUp(v, du + dv - d);
    } else {
      return -1;
    }
  }
  // [u, v) or [u, v]
  template <class F> void doPathUp(int u, int v, bool inclusive, F f) const {
    assert(contains(v, u));
    for (; head[u] != head[v]; u = par[head[u]]) f(dis[head[u]], dis[u] + 1);
    if (inclusive) {
      f(dis[v], dis[u] + 1);
    } else {
      if (v != u) f(dis[v] + 1, dis[u] + 1);
    }
  }
  // not path order, include lca(u, v) or not
  template <class F> void doPath(int u, int v, bool inclusive, F f) const {
    const int l = lca(u, v);
    doPathUp(u, l, false, f);
    doPathUp(v, l, inclusive, f);
  }

  // (vs, ps): compressed tree
  // vs: DFS order (sorted by dis)
  // vs[ps[x]]: the parent of vs[x]
  // ids[vs[x]] = x, not set for non-tree vertex
  vector<int> ids;
  pair<vector<int>, vector<int>> compress(vector<int> us) {
    // O(n) first time
    ids.resize(n, -1);
    std::sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (dis[u] < dis[v]);
    });
    us.erase(std::unique(us.begin(), us.end()), us.end());
    int usLen = us.size();
    assert(usLen >= 1);
    for (int x = 1; x < usLen; ++x) us.push_back(lca(us[x - 1], us[x]));
    std::sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (dis[u] < dis[v]);
    });
    us.erase(std::unique(us.begin(), us.end()), us.end());
    usLen = us.size();
    for (int x = 0; x < usLen; ++x) ids[us[x]] = x;
    vector<int> ps(usLen, -1);
    for (int x = 1; x < usLen; ++x) ps[x] = ids[lca(us[x - 1], us[x])];
    return make_pair(us, ps);
  }
};

////////////////////////////////////////////////////////////////////////////////


constexpr Int INF = 2001001001001001001LL;

// a + b x
// b: decreasing
// x: increasing
struct Cht {
  int head;
  vector<pair<Int, Int>> ps;
  Cht() : head(0) {}
  void add(Int a, Int b) {
    for (; (int)ps.size() - head >= 2; ps.pop_back()) {
      const Int a2 = ps[ps.size() - 2].first, b2 = ps[ps.size() - 2].second;
      const Int a1 = ps[ps.size() - 1].first, b1 = ps[ps.size() - 1].second;
      if ((__int128)(a1 - a2) * (b1 - b) < (__int128)(a - a1) * (b2 - b1)) break;
    }
    ps.emplace_back(a, b);
// cerr<<"ps = "<<ps<<endl;
  }
  Int get(Int x) {
    for (; (int)ps.size() - head >= 2 && ps[head].first + ps[head].second * x >= ps[head + 1].first + ps[head + 1].second * x; ++head) {}
    if ((int)ps.size() - head == 0) return INF;
    return ps[head].first + ps[head].second * x;
  }
};

Int M;
int N, Q;
vector<Int> D;
vector<int> A, B;
vector<Int> C;
vector<Int> L;
vector<int> S, T;

vector<vector<int>> G;


namespace brute {
Int dist[5010][5010];
void dfs(int r, int u, int p, Int d) {
  dist[r][u] = d;
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (p != v) {
      dfs(r, v, u, d + C[i]);
    }
  }
}
vector<Int> run() {
  for (int r = 0; r < N; ++r) {
    dfs(r, r, -1, 0);
  }
  vector<Int> ans(Q, INF);
  for (int q = 0; q < Q; ++q) {
    for (int u = 0; u < N; ++u) {
      chmin(ans[q], dist[S[q]][u] + L[q] * D[u] + dist[T[q]][u]);
    }
  }
  return ans;
}
}  // brute


namespace sub3 {
vector<Int> cs, dp;
void dfs(Int l, int u, int p, Int c) {
  cs[u] = c;
  dp[u] = l * D[u];
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (p != v) {
      dfs(l, v, u, c + C[i]);
      chmin(dp[u], 2 * C[i] + dp[v]);
    }
  }
}
int segN;
vector<Int> segs[2];
Int get(int h, int a, int b) {
  Int ret = INF;
  for (a += segN, b += segN; a < b; a >>= 1, b >>= 1) {
    if (a & 1) chmin(ret, segs[h][a++]);
    if (b & 1) chmin(ret, segs[h][--b]);
  }
  return ret;
}
vector<Int> run() {
  const int rt = 0;
  Hld hld(N);
  for (int i = 0; i < N - 1; ++i) hld.ae(A[i], B[i]);
  hld.build(rt);
// cerr<<hld<<flush;
  for (segN = 1; segN < N; segN <<= 1) {}
  for (int h = 0; h < 2; ++h) {
    segs[h].assign(segN << 1, INF);
  }
  
  vector<vector<int>> qss(M);
  for (int q = 0; q < Q; ++q) {
    qss[L[q]].push_back(q);
  }
  vector<Int> ans(Q, INF);
  for (Int l = 0; l < M; ++l) {
    cs.assign(N, 0);
    dp.assign(N, INF);
    dfs(l, rt, -1, 0);
// cerr<<"l = "<<l<<", cs = "<<cs<<", dp = "<<dp<<endl;
    for (int j = 0; j < N; ++j) {
      const int u = hld.sid[j];
      segs[0][segN + j] = dp[u];
      segs[1][segN + j] = dp[u] - 2 * cs[u];
    }
    for (int h = 0; h < 2; ++h) {
      for (int a = segN; --a; ) {
        segs[h][a] = min(segs[h][a << 1], segs[h][a << 1 | 1]);
      }
    }
    for (const int q : qss[l]) {
      const int s = S[q], t = T[q];
      const int u = hld.lca(s, t);
      hld.doPathUp(s, u, false, [&](int a, int b) -> void {
        chmin(ans[q], get(0, a, b));
      });
      hld.doPathUp(t, u, false, [&](int a, int b) -> void {
        chmin(ans[q], get(0, a, b));
      });
      hld.doPathUp(u, rt, true, [&](int a, int b) -> void {
        chmin(ans[q], get(1, a, b) + 2 * cs[u]);
      });
      ans[q] += (cs[s] - cs[u]) + (cs[t] - cs[u]);
    }
  }
  return ans;
}
}  // sub3


namespace sub4 {
vector<int> dep;
vector<Int> cs;
void dfs(int u, int p, int d, Int c) {
  dep[u] = d;
  cs[u] = c;
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (p != v) {
      dfs(v, u, d + 1, c + C[i]);
    }
  }
}
int segN;
vector<Cht> segs[3];
Int get(int h, int a, int b, Int x) {
  Int ret = INF;
  for (a += segN, b += segN; a < b; a >>= 1, b >>= 1) {
    if (a & 1) chmin(ret, segs[h][a++].get(x));
    if (b & 1) chmin(ret, segs[h][--b].get(x));
  }
  return ret;
}
vector<Int> run() {
  dep.assign(N, -1);
  cs.assign(N, 0);
  for (int u = 0; u < N; ++u) if (G[u].size() == 1) {
    dfs(u, -1, 0, 0);
    break;
  }
// cerr<<"dep = "<<dep<<", cs = "<<cs<<endl;
  for (segN = 1; segN < N; segN <<= 1) {}
  for (int h = 0; h < 3; ++h) {
    segs[h].assign(segN << 1, Cht());
  }
  {
    vector<int> us(N);
    for (int u = 0; u < N; ++u) us[u] = u;
    sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (D[u] > D[v]);
    });
    for (const int u : us) {
      for (int a = segN + dep[u]; a; a >>= 1) {
        segs[0][a].add(- cs[u] - cs[u], D[u]);
        segs[1][a].add(+ cs[u] - cs[u], D[u]);
        segs[2][a].add(+ cs[u] + cs[u], D[u]);
      }
    }
  }
  vector<Int> ans(Q, INF);
  {
    vector<int> qs(Q);
    for (int q = 0; q < Q; ++q) qs[q] = q;
    sort(qs.begin(), qs.end(), [&](int q0, int q1) -> bool {
      return (L[q0] < L[q1]);
    });
    for (const int q : qs) {
      int s = S[q], t = T[q];
      int x = dep[s], y = dep[t];
      if (x > y) {
        swap(s, t);
        swap(x, y);
      }
      chmin(ans[q], + cs[s] + get(0, 0, x,     L[q]) + cs[t]);
      chmin(ans[q], - cs[s] + get(1, x, y + 1, L[q]) + cs[t]);
      chmin(ans[q], - cs[s] + get(2, y + 1, N, L[q]) - cs[t]);
    }
  }
  return ans;
}
}  // sub4


namespace sub5 {
vector<Int> run() {
  int r = -1;
  for (int u = 0; u < N; ++u) if ((int)G[u].size() == N - 1) {
    r = u;
    break;
  }
  vector<Int> cs(N, 0);
  for (int i = 0; i < N - 1; ++i) {
    cs[A[i] ^ B[i] ^ r] = C[i];
  }
// cerr<<"r = "<<r<<", cs = "<<cs<<endl;
  Cht cht;
  {
    vector<int> us(N);
    for (int u = 0; u < N; ++u) us[u] = u;
    sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (D[u] > D[v]);
    });
    for (const int u : us) {
      cht.add(2 * cs[u], D[u]);
    }
  }
  vector<Int> ans(Q, INF);
  {
    vector<int> qs(Q);
    for (int q = 0; q < Q; ++q) qs[q] = q;
    sort(qs.begin(), qs.end(), [&](int q0, int q1) -> bool {
      return (L[q0] < L[q1]);
    });
    for (const int q : qs) {
      if (S[q] == T[q]) {
        chmin(ans[q], D[S[q]] * L[q]);
      } else {
        chmin(ans[q], D[S[q]] * L[q] + cs[S[q]] + cs[T[q]]);
        chmin(ans[q], cs[S[q]] + cs[T[q]] + D[T[q]] * L[q]);
      }
      chmin(ans[q], cs[S[q]] + cht.get(L[q]) + cs[T[q]]);
    }
  }
  return ans;
}
}  // sub5


int main() {
  for (; ~scanf("%d%lld%d", &N, &M, &Q); ) {
    D.resize(N);
    for (int u = 0; u < N; ++u) {
      scanf("%lld", &D[u]);
    }
    A.resize(N - 1);
    B.resize(N - 1);
    C.resize(N - 1);
    for (int i = 0; i < N - 1; ++i) {
      scanf("%d%d%lld", &A[i], &B[i], &C[i]);
      --A[i];
      --B[i];
    }
    L.resize(Q);
    S.resize(Q);
    T.resize(Q);
    for (int q = 0; q < Q; ++q) {
      Int s, t;
      scanf("%lld%lld", &s, &t);
      --s;
      --t;
      L[q] = abs(s / N - t / N);
      S[q] = s % N;
      T[q] = t % N;
    }
    
    G.assign(N, {});
    for (int i = 0; i < N - 1; ++i) {
      G[A[i]].push_back(i);
      G[B[i]].push_back(i);
    }
    
    vector<int> freqDeg(N, 0);
    for (int u = 0; u < N; ++u) {
      ++freqDeg[G[u].size()];
    }
    
    vector<Int> ans;
    if (M <= 20) {
      ans = sub3::run();
    } else if (freqDeg[1] <= 2) {
      ans = sub4::run();
    } else if (freqDeg[N - 1] >= 1) {
      ans = sub5::run();
    } else {
      ans = brute::run();
    }
    for (int q = 0; q < Q; ++q) {
      printf("%lld\n", ans[q]);
    }
#ifdef LOCAL
const auto brt=brute::run();
cerr<<"brt = "<<brt<<endl;
cerr<<"ans = "<<ans<<endl;
assert(brt==ans);
#endif
  }
  return 0;
}