#include <bits/stdc++.h>
//#pragma GCC optimize ("Ofast,unroll-loops")
//#pragma GCC target ("avx2")
using namespace std;
typedef long long ll;
typedef pair<int, int> pp;
#define rep(i,l,r) for(int i = (l); i < (r); i++)
#define per(i,r,l) for(int i = (r); i >= (l); i--)
#define all(x) begin(x), end(x)
#define sz(x) (int)x.size()
#define pb push_back
#define ff first
#define ss second
void dbg(){
cerr << endl;
}
template<typename Head, typename... Tail> void dbg(Head h, Tail... t){
cerr << " " << h << ",";
dbg(t...);
}
#define er(...) cerr << __LINE__ << " <" << #__VA_ARGS__ << ">:", dbg(__VA_ARGS__)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void IOS(){
cin.tie(0) -> sync_with_stdio(0);
// #ifndef ONLINE_JUDGE
// freopen("inp.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
// #endif
}
const ll mod = 1e9 + 7, maxn = 5e5 + 5, maxm = 20, inf = ll(1e9) + 5;
ll pw(ll a, ll b){
if(!b) return 1;
ll k = pw(a, b>>1ll);
return k*k%mod*(b&1ll?a:1ll)%mod;
}
vector<int> adj[maxn];
ll fac[maxn], inv[maxn];
ll C(int n, int r){
if(r < 0 || r > n) return 0;
return fac[n]*inv[r]%mod*inv[n-r]%mod;
}
int main(){ IOS();
fac[0] = inv[0] = 1;
rep(i,1,maxn){
fac[i] = fac[i-1]*i%mod;
inv[i] = pw(fac[i], mod-2);
}
int n, r; cin >> n >> r;
rep(i,1,n){
int u, v; cin >> u >> v; u--, v--;
adj[u].pb(v), adj[v].pb(u);
}
int q; cin >> q;
cout << C(r + n - 1, n - 1) << '\n';
return 0;
}
