#include <iostream>
#include <functional>
#include <vector>

using namespace std;

typedef long double ld;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    int z;
    cin >> z;
    while (z--) {
        int n, c;
        cin >> n >> c;
        
        vector<vector<int>> G(n);
        for (int i = 0; i < n - 1; i++) {
            int u, v;
            cin >> u >> v;
            --u, --v;
            G[u].push_back(v);
            G[v].push_back(u);
        }

        vector<int> P(n);
        function<void(int, int)> DFS = [&](int u, int p) {
            P[u] = p;
            for (auto& v : G[u])
                if (v != p) DFS(v, u);
        };

        DFS(0, n);

        vector<pair<ld, ld>> V(n + 1);
        V[c - 1].first = 1;

        ld res = 0;

        int m;
        cin >> m;
        while (m--) {
            int a;
            cin >> a; --a;
            ld v = V[a].first + V[P[a]].second;
            if (v == 0) continue;
            res += v;
            ld r = v / G[a].size();
            V[a].second += r;
            V[P[a]].first += r;
            V[a].first = 0;
        }

        cout << res << '\n';
    }
}