// UUID: fd4a6981-f927-4fe2-891b-55d536a77736
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
vector<vector<pair<int, int> > > g;
vector<vector<int> > eg;
const int MOD = 1e9 + 7;
vector<int> path;
vector<bool> vis;
void con(int v)
{
vis[v] = 1;
for(auto x : eg[v]) if(!vis[x]) con(x);
}
bool dfs(int v, int p, int go)
{
if(v == go) return 1;
for(auto [x, ind] : g[v])
{
if(x == p) continue;
path.push_back(ind);
if(dfs(x, v, go)) return 1;
}
if(!path.empty()) path.pop_back();
return 0;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
ll n, m, k;
cin >> n >> m >> k;
g.resize(n + 1);
eg.resize(n);
for(int i = 0; i < n - 1; i++)
{
int x, y;
cin >> x >> y;
g[x].push_back({y, i});
g[y].push_back({x, i});
}
vector<vector<pair<int, int> > > pa(m);
for(int i = 0; i < m; i++)
{
path.clear();
int a, b;
cin >> a >> b;
dfs(a, -1, b);
for(int j = 0; j < path.size() - 1; j++)
{
pa[i].push_back({path[j], path[j + 1]});
}
}
ll ans = 0;
const int e = 1 << m;
for(int i = 0; i < e; i++)
{
eg.assign(n, {});
vis.assign(n, {});
for(int j = 0; j < m; j++)
{
if((i >> j) & 1)
{
for(auto [x, y] : pa[j])
{
eg[x].push_back(y);
eg[y].push_back(x);
}
}
}
ll val = 1;
for(int j = 0; j < n - 1; j++)
{
if(!vis[j])
{
con(j);
val *= k;
val %= MOD;
}
}
if(__builtin_popcount(i) % 2 == 0) ans += val;
else ans -= val;
ans %= MOD;
}
cout << (ans + MOD) % MOD;
}
