#include<cstdio>
#define fo(i,x,y) for(int i = x;i <= y;++i)
#define fd(i,x,y) for(int i = x;i >= y;--i)
#define _is 1048576 * 10
#define _os 1048576 * 10
#define gc() ib[++bi]
#define pc(ch) ob[++bo] = ch
#define ll long long
#define inf 4000000000000000000ll
using namespace std;
char ib[_is],ob[_os];int bi = -1,bo = -1;
int rd()
{
	int x = 0;char ch = gc();
	while(ch < 48 || ch > 57) ch = gc();
	while(ch >= 48 && ch <= 57) x = x * 10 + ch - 48,ch = gc();
	return x;
}
void pr(ll x)
{
	char ch[20];int w = -1;
	if(x == 0) ch[++w] = 48;
	while(x) ch[++w] = x % 10 + 48,x /= 10;
	fd(i,w,0) pc(ch[i]);pc('\n');
}
int n,q,m,e[400010][2],lst[200010],tot,x,y,v[200010],f[200010][18],d[200010],Fa[200010],s[200010];
void add(int x,int y) {e[++tot][0] = y,e[tot][1] = lst[x],lst[x] = tot;}
void Mi(ll &x,ll y) {if(y < x) x = y;}
void Mi(int &x,int y) {if(y < x) x = y;}
struct mat{ll a[3][3];}F[200010][18],G[200010][18],C;
struct vec{ll a[3];}c,ans;
int id[20][2];
mat operator * (mat &A,mat &B)
{
	fo(i,0,m) fo(j,0,m) C.a[i][j] = inf;
	fo(i,0,m) fo(k,0,m)
	{
		if(A.a[i][k] == inf) continue;
		fo(j,0,m) Mi(C.a[i][j],A.a[i][k] + B.a[k][j]);
	}
	return C;
}
vec operator * (mat &A,vec &B)
{
	fo(i,0,m) c.a[i] = inf;
	fo(i,0,m) fo(k,0,m) Mi(c.a[i],A.a[i][k] + B.a[k]);
	return c;
}
void dg(int x,int fa)
{
	Fa[x] = f[x][0] = fa,d[x] = d[fa] + 1;
	fo(i,1,17) f[x][i] = f[f[x][i - 1]][i - 1];
	if(m == 0) F[x][0].a[0][0] = v[x];
	else if(m == 1) F[x][0].a[0][0] = F[x][0].a[0][1] = v[x],F[x][0].a[1][0] = 0,F[x][0].a[1][1] = inf;
	else
	{
		fo(i,1,2) fo(j,0,2) F[x][0].a[i][j] = inf;
		fo(i,0,2) F[x][0].a[0][i] = v[x];
		F[x][0].a[1][0] = F[x][0].a[2][1] = 0,F[x][0].a[1][1] = s[x];
	}
	G[x][0] = F[x][0];
	fo(i,1,17) F[x][i] = F[f[x][i - 1]][i - 1] * F[x][i - 1],G[x][i] = G[x][i - 1] * G[f[x][i - 1]][i - 1];
	for(int i = lst[x];i;i = e[i][1]) if(e[i][0] ^ fa) dg(e[i][0],x);
}
int main()
{
	fread(ib,1,_is,stdin);
	n = rd(),q = rd(),m = rd() - 1;
	fo(i,1,n) v[i] = rd(),s[i] = 1000000000;
	fo(i,1,n - 1) x = rd(),y = rd(),add(x,y),add(y,x),Mi(s[x],v[y]),Mi(s[y],v[x]);
	dg(1,0);
	while(q--)
	{
		x = rd(),y = rd();
		if(d[x] < d[y]) x ^= y ^= x ^= y;
		fo(i,0,m - 1) ans.a[i] = inf;ans.a[m] = 0;
		fd(i,17,0) if(d[f[x][i]] >= d[y]) ans = F[x][i] * ans,x = f[x][i];
		if(x == y) ans = F[x][0] * ans;
		else
		{
			int tp = 0;
			fd(i,17,0) if(f[x][i] && f[y][i] && f[x][i] != f[y][i]) ans = F[x][i] * ans,id[++tp][0] = y,id[tp][1] = i,x = f[x][i],y = f[y][i];
			ans = F[x][1] * ans,ans = G[y][0] * ans;
			fd(i,tp,1) ans = G[id[i][0]][id[i][1]] * ans;
		}
		pr(ans.a[0]);		
	}
	fwrite(ob,1,bo + 1,stdout);
	return 0;
}