// Skyqwq
#include <bits/stdc++.h>

#define pb push_back
#define fi first
#define se second
#define mp make_pair

using namespace std;

typedef long long LL;
typedef pair<int, int> PII;

template <typename T> bool chkMax(T &x, T y) { return (y > x) ? x = y, 1 : 0; }
template <typename T> bool chkMin(T &x, T y) { return (y < x) ? x = y, 1 : 0; }

template <typename T> void inline read(T &x) {
    int f = 1; x = 0; char s = getchar();
    while (s < '0' || s > '9') { if (s == '-') f = -1; s = getchar(); }
    while (s <= '9' && s >= '0') x = x * 10 + (s ^ 48), s = getchar();
    x *= f;
}

const int N = 65, P = 1e9 + 7;

int n, m, k, fa[N], d[N], fw[N], f[N];

vector<PII> g[N];

void dfs(int u) {
	for (PII o: g[u]) {
		int v = o.fi;
		if (v == fa[u]) continue;
		d[v] = d[u] + 1, fa[v] = u, fw[v] = o.se;
		dfs(v);
	}
}

vector<int> b[N];

void inline work(int x, int y, int k) {
	while (x != y) {
		if (d[x] < d[y]) swap(x, y);
		b[k].pb(fw[x]);
		x = fa[x];
	}
}

int find(int x) {
	return f[x] == x ? x : f[x] = find(f[x]);
}

void inline add(int &x, int y) {
	x += y;
	if (x >= P) x -= P;
}

void inline del(int &x, int y) {
	x -= y;
	if (x < 0) x += P;
}

int main() {
	read(n), read(m), read(k);
	for (int i = 1, u, v; i < n; i++) {
		read(u), read(v);
		g[u].pb(mp(v, i)), g[v].pb(mp(u, i));
	}
	dfs(1);
	for (int i = 0; i < m; i++) {
		int u, v; read(u), read(v);
		work(u, v, i);
	}
	int ans = 0;
	for (int i = 0; i < (1 << m); i++) {
		int c = 0;
		for (int j = 1; j < n; j++) f[j] = j;
		for (int j = 0; j < m; j++) {
			if (i >> j & 1) {
				for (int k: b[j])
					f[find(k)] = find(b[j][0]);
				c ^= 1;
			}
		}
		int v = 1;
		for (int j = 1; j < n; j++)
			if (find(j) == j) v = 1ll * v * k % P;
		if (c) del(ans, v);
		else add(ans, v);	
	}
	printf("%d\n", ans);
    return 0;
}