#include <bits/stdc++.h>

#define rep(i,a,b) for(int i = a; i < (b); ++i)
#define sz(x) (int)(x).size()

using namespace std;

using ll = long long;
using pi = pair<int, int>;
using vi = vector<int>;

struct op {
	int from;
	int to;
	int count;
};

void solve() {
	int n;
	cin >> n;
	vector<vector<int>> neighs(n);
	vector<vector<int>> flows(n);
	vi lants(n);
	vi pars(n, -1);
	for (int i = 0; i < n-1; i++) {
		int a,b;
		cin >> a >> b;
		neighs[a].push_back(b);
		flows[a].push_back(0);
		neighs[b].push_back(a);
		flows[b].push_back(0);
	}
	int k;
	cin >> k;
	for (int i = 0; i < k; ++i) {
		int ix;
		cin >> ix;
		lants[ix] = 1;
	}
	vi target(n);
	for (int  i = 0; i < k; ++ i){
		int ix;
		cin >> ix;
		target[ix] = 1;
	}

	queue<int> leaves;
	vector<int> conns(n);
	for (int i = 0; i < n; ++i) {
		if (neighs[i].size() == 1) leaves.push(i);
		conns[i] = neighs[i].size();
	}

	int root = -1;
	vector<op> ops;
	while (!leaves.empty()) {
		int leaf = leaves.front();
		leaves.pop();
		lants[leaf] -= target[leaf];
		assert(pars[leaf] == -1);
		bool par_found = false;
		for (int o : neighs[leaf]) {
			if (pars[o] == leaf) continue;
			par_found = true;
			lants[o] += lants[leaf];
			pars[leaf] = o;
			if (lants[leaf] > 0) {
				ops.push_back({leaf, o, lants[leaf]});
				lants[leaf] = 0;
			}
			conns[o] -= 1;
			if (conns[o] == 1) {
				leaves.push(o);
			}
		}
		if (!par_found) {
			root = leaf;
			assert(leaves.empty());
		}
	}
	leaves.push(root);
	while (!leaves.empty()) {
		int leaf = leaves.front();
		leaves.pop();
		for (int o : neighs[leaf]) {
			if (o == pars[leaf]) continue;
			if (lants[o] < 0) {
				ops.push_back({leaf, o, -lants[o]});
			}
			leaves.push(o);
		}
	}
	cout << ops.size() << "\n";
	for (const auto& o : ops) {
		cout << o.from << " " << o.to << " " << o.count << "\n";
	}


}

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

	solve();
}