#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using vi = vector<int>;

vector<vi> adj;
vi need;
vi black, white;
vector<tuple<int, int, int>> res;

void needdfs(int a, int p) {
    need[a] = white[a] - black[a];
    for (auto &&b : adj[a]) if(b != p) {
        needdfs(b, a);
        need[a] += need[b];
    }
}

void resdfs(int a, int p, bool up) {
    if(need[a] < 0 && !up) {
        res.push_back({p, a, -need[a]});
    }
    for (auto &&b : adj[a]) if(b != p) {
        resdfs(b, a, up);
    }
    if(need[a] > 0 && up) {
        res.push_back({a, p, need[a]});
    }
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    ll n; cin >> n;
    adj.assign(n, {});
    need = black = white = vi(n, 0);

    for (int i = 0; i < n-1; i++) {
        int a, b; cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    int k; cin >> k;
    for (int i = 0; i < k; i++) {
        int a; cin >> a;
        white[a] = 1;
    }
    for (int i = 0; i < k; i++) {
        int a; cin >> a;
        black[a] = 1;
    }
    
    needdfs(0, 0);
    
    resdfs(0, 0, true);
    resdfs(0, 0, false);

    cout << res.size() << "\n";
    for (auto [a, b, n] : res) {
        cout << a << " " << b << " " << n << "\n";
    }
}