题解

#include<bits/stdc++.h>
#define pb push_back
using namespace std;
typedef long long ll;
typedef pair<int, int> PII;
template<typename T> inline void read(T &x){
	x = 0; bool F = 0; char c = getchar();
	for (;!isdigit(c);c = getchar()) if (c == '-') F = 1;
	for (;isdigit(c);c = getchar()) x = x*10+(c^48);
	if (F) x = -x;
}
template<typename T1, typename... T2> inline void read(T1 &x, T2 &...y){read(x); read(y...);}
template<typename T> inline void checkmax(T &a, const T &b){if (a<b) a = b;}
template<typename T> inline void checkmin(T &a, const T &b){if (a>b) a = b;}
const int N = 1e5+5;
const ll MOD = 1e9+7;
int n, m, u[N], v[N], flag_edge[N], d[N];
vector<PII> to[N];
ll sum[N][2], inv[N], ans;

void dfs(int u, int fa){
	sum[u][0] = sum[u][1] = 0;
	int v;
	ll val = 0;
	for (auto x: to[u]){
		v = x.first; if (v == fa) continue;
		dfs(v, u);
		if (x.second) sum[v][1] += sum[v][0], sum[v][0] = 0;
		(val += sum[v][1]*(sum[u][0]+sum[u][1]) + sum[v][0]*sum[u][1]) %= MOD;
		(sum[u][0] += sum[v][0]) %= MOD;
		(sum[u][1] += sum[v][1]) %= MOD;
	}
	ll INV = inv[d[u]];
	(ans += val*INV) %= MOD;
	if (!d[u]) sum[u][0]++;
	(sum[u][0] *= INV) %= MOD;
	(sum[u][1] *= INV) %= MOD;
}
inline void solve(){
	read(n, m); for (int i = 1;i<=n;i++) d[i] = -1, to[i].clear(); ans = 0;
	for (int i = 1;i<n;i++) read(u[i], v[i]), flag_edge[i] = 0, d[u[i]]++, d[v[i]]++;
	int t; while (m--) read(t), flag_edge[t] = 1;
	if (n == 2){printf("1\n"); return;}
	for (int i = 1;i<n;i++) to[u[i]].pb({v[i], flag_edge[i]}), to[v[i]].pb({u[i], flag_edge[i]});
	int rt = 0; for (int i = 1;i<=n;i++) if (d[i]) rt = i;
	dfs(rt, 0);
	for (int i = 1;i<=n;i++){
		for (int j = 1;j<=d[i];j++) (ans *= j) %= MOD;
	}
	printf("%lld\n", ans);
}
int main(){
	inv[0] = inv[1] = 1; for (int i = 2;i<N;i++) inv[i] = inv[MOD%i]*(MOD-MOD/i)%MOD;
	int c, t; read(c, t); while (t--) solve();
	return 0;
}