#include<bits/stdc++.h>
using namespace std;
typedef long double D;
#define pb push_back
const int N = 1000011;
vector<int> e[N];
D dp[N];
int q[50000055];
void solve() {
	int n, c;
	scanf("%d%d", &n, &c);
	for(int i = 1; i < n; i++) {
		int x, y;
		scanf("%d%d", &x, &y);
		e[x].pb(y);
		e[y].pb(x);
	}
	int Q;
	scanf("%d", &Q);
	for(int i = 1; i <= Q; i++) {
		scanf("%d", &q[i]);
	}
	for(int i = 1; i <= n; i++) {
		dp[i] = 0;
	}
	for(int i = Q; i >= 1; i--) {
		int v = q[i];
		dp[v] = 1;
		for(int y : e[v]) {
			dp[v] += 1. / (D)(e[v].size()) * dp[y];
		}
	}
	printf("%.12f\n", (double)dp[c]);
	for(int i = 1; i <= n; i++) {
		e[i].clear();
	}
}
int main() {
	int t;
	scanf("%d", &t);
	for(int i = 0; i < t; i++) {
		solve();
	}
}