#include <bits/stdc++.h>
#include <cassert>
using namespace std;
using ll = long long;
// #define int ll

int n, k;
constexpr int MAXN = 200'000;
vector<int> adj[MAXN];
int s1[MAXN], s2[MAXN], V[MAXN];

struct Elem {
    Elem(int ff, int tt, int vv) : f(ff), t(tt), v(vv) {}
    int f, t, v;
};

vector<Elem> ans;

void dfs1(int v, int p) {
    for (auto x : adj[v]) {
        if (x == p) continue;
        dfs1(x, v);
    }
    if (s1[v]) V[v]++;
    if (s2[v]) V[v]--;

    if (V[v] > 0) {
        ans.emplace_back(v, p, V[v]);
    }
    V[p] += V[v];
}

void dfs2(int v, int p) {
    for (auto x : adj[v]) {
        if (x == p) continue;
        if (V[x] < 0) {
            ans.emplace_back(v, x, -V[x]);
        }
        dfs2(x, v);
    }
}

int find_leaf() {
    int v = 0, p = 0;
    while (adj[v].size() != 1) {
        if (adj[v][0] != p) {
            p = v;
            v = adj[v][0];
        } else {
            p = v;
            v = adj[v][1];
        }
    }
    return v;
}

signed main() {
    cin >> n;
    for (int i = 1; i < n; i++) {
        int x, y;
        cin >> x >> y;
        adj[x].push_back(y);
        adj[y].push_back(x);
    }
    cin >> k;
    for (auto A : {s1, s2}) {
        for (int i = 0; i < k; i++) {
            int x;
            cin >> x;
            A[x] = 1;
        }
    }
    int v = find_leaf();
    dfs1(v, v);
    // for (int i = 0; i < n; i++) {
    //     cout << V[i] << ' ';
    // }
    // cout << endl;
    dfs2(v, v);
    cout << ans.size() << endl;
    for (auto [f, t, v] : ans) {
        cout << f << ' ' << t << ' ' << v << endl;
    }
}