#include <bits/stdc++.h>
using namespace std;
void main_program();
signed main(){
ios_base::sync_with_stdio(0); cin.tie(0);
main_program();
}
#define int long long
const int mod = 1e9 + 7;
struct DSU{
vector<int> parent, size;
DSU(int N){
parent.resize(N); iota(parent.begin(), parent.end(), 0);
size.assign(N, 1);
}
int get(int x){
return (x == parent[x]) ? x : (parent[x] = get(parent[x]));
}
bool merge(int a, int b){
a = get(a); b = get(b);
if (a == b) return false;
if (size[a] < size[b]) swap(a, b);
parent[b] = a; size[a] += size[b];
return true;
}
};
int binpow(int n, int a){
int res = 1;
for (int exp = n; a; a >>= 1, exp = exp * exp % mod){
if (a & 1) res = res * exp % mod;
}
return res;
}
int n, m, K;
vector<int> crr;
vector<vector<int>> lst;
vector<vector<pair<int, int>>> adj;
vector<pair<int, int>> qs;
void dfs(int x, int target, int p = -1){
if (x == target) lst.push_back(crr);
for (auto [k, idx]: adj[x]){
if (k == p) continue;
crr.push_back(idx);
dfs(k, target, x);
crr.pop_back();
}
}
void main_program(){
cin >> n >> m >> K;
adj.resize(n);
qs.resize(m);
for (int i = 0; i < n-1; i++){
int a, b; cin >> a >> b;
a--; b--;
adj[a].emplace_back(b, i);
adj[b].emplace_back(a, i);
}
for (int i = 0; i < m; i++){
int c, d; cin >> c >> d;
c--; d--;
qs[i] = {c, d};
}
for (auto [x, y]: qs) dfs(x, y);
int res = 0;
for (int mask = 0; mask < (1 << m); mask++){
DSU dsu(n-1);
int cc = n-1;
for (int i = 0; i < m; i++){
if ((mask >> i) & 1){
for (int j = 1; j < (int)lst[i].size(); j++){
if (dsu.merge(lst[i][j-1], lst[i][j])) cc--;
}
}
}
int sign = (__builtin_popcountll(mask) & 1) ? -1 : 1;
res += sign * binpow(K, cc);
res %= mod;
}
cout << (res % mod + mod) % mod << "\n";
}
