#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using pii = pair<int,int>;
using vll = vector<ll>;
using str = string;
using vstr = vector<string>;

#define PB push_back
#define ALL(x) (x).begin() (x).end()
#define FOR(i,s,f) for(int (i) = (s); i < (f); i++)


int main(){
    int n;
    cin >>n;
    vector<set<int>> mp(n);
    vector<map<int,int>> precom(n); 
    FOR(i,0,n-1){
        int x,y;
        cin >>x>>y;
        mp[x].insert(y);
        mp[y].insert(x);
    }
    vi zaciatok(n);
    vi koniec(n);
    int zas;
    cin >>zas;
    FOR(i,0,zas){
        int x; cin >>x;
        zaciatok[x] = 1;
    }
    FOR(i,0,zas){
        int x; cin >>x;
        koniec[x] = 1;
    }

    queue<int> q;
    FOR(i,0,n){
        if(mp[i].size() == 1) q.push(i);
    }

    vi stav(n, 0);
    vi vis(n,0);

    vi nesprac_deti(n);FOR(i,0,n){
        nesprac_deti[i] = mp[i].size();
    }

    while(!q.empty()){
        int cur = q.front();
        q.pop();
        if(vis[cur] == 1) continue;
        vis[cur] = 1;
        if(zaciatok[cur] == 1 and koniec[cur] == 0) stav[cur]++;
        if(zaciatok[cur] == 0 and koniec[cur] == 1) stav[cur]--;


        for(auto to : mp[cur]){
            if(vis[to] == 0){
                if (stav[cur] > 0)
                    precom[cur][to] = stav[cur];
                else
                    precom[to][cur] = -stav[cur];
                stav[to] += stav[cur];
            }
            nesprac_deti[to] --;
            if(nesprac_deti[to] <= 1) q.push(to);
        }
    }

    vi dodavky(n);
    FOR(i,0,n){
        for(auto j :precom[i]) dodavky[j.first] ++;
    }
    FOR(i,0,n) if(dodavky[i] == 0) q.push(i);


    vvi answer;
    FOR(i,0,n) vis[i] = 0;
    while(!q.empty()){
        int cur = q.front();
        q.pop();
        if(vis[cur]) continue;
        vis[cur] = 1;


        for(auto j : precom[cur]){
            answer.PB({cur, j.first,j.second});
            dodavky[j.first]--;
            if(dodavky[j.first] == 0) q.push(j.first);
        }
    }
    
    

    cout <<answer.size() <<'\n';
    for(auto j : answer){
        cout << j[0] <<" " <<j[1]<< " " << j[2] <<"\n";
    }

}