#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;

#define For(i, a, n) for(ll i=a;i<n;i++)
#define vec vector
#define sz(x) (ll)x.size()
#define all(x) begin(x), end(x)

template<class A, class B>
pair<A, B>operator+(const pair<A, B>&a, const pair<A, B>&b){
    return {a.first + b.first, a.second + b.second};
}

template<class A, class B>
ostream&operator<<(ostream&os, const pair<A, B>&p){
    return os<<"("<<p.first<<", "<<p.second<<")";
}

template<class A, class B, class C>
basic_ostream<A, B>&operator<<(basic_ostream<A, B>&os, const C&c){
    for(auto i=begin(c);i!=end(c);++i){
        os<<(i==begin(c)?"":" ")<<*i;
    }
    return os;
}

template<typename... Args>
void dbg(Args&&... args){
    ((cerr<<args<<" |"),...);
    cerr<<endl;
}

void countlanterns(vec<ll>& counts, vec<vec<ll>>& children, vec<bool>& values, ll start){
    for(ll i = 0; i < children[start].size(); i++){
        countlanterns(counts,children,values,children[start][i]);
        counts[start] += counts[children[start][i]];
    }
    if(values[start]){
        counts[start]++;
    }
}

void f(ll pos, vec<pair<pll,ll>>& solution, vec<vec<ll>>& children, vec<ll>& parents, vec<ll>& v, vec<bool>& goal){
    //excess children
    for(ll i = 0; i < children[pos].size(); i++){
        ll child = children[pos][i];
        if(v[child] <= 0){
            continue;
        }
        f(child,solution,children,parents,v,goal);
    }
    //take
    for(ll i = 0; i < children[pos].size(); i++){
        ll child = children[pos][i];
        if(v[child] > 0){
            solution.push_back({{child,pos},v[child]});
        }
    }
    //give
    for(ll i = 0; i < children[pos].size(); i++){
        ll child = children[pos][i];
        if(v[child] < 0){
            solution.push_back({{pos,child},-v[child]});
        }
    }
    //carrying children
    for(ll i = 0; i < children[pos].size(); i++){
        ll child = children[pos][i];
        if(v[child] > 0){
            continue;
        }
        if(goal[child]){
            f(child,solution,children,parents,v,goal);
        }
    }

    //non-carrying children
    for(ll i = 0; i < children[pos].size(); i++){
        ll child = children[pos][i];
        if(v[child] > 0){
            continue;
        }
        if(!goal[child]){
            f(child,solution,children,parents,v,goal);
        }
    }
}

void solve(){

    ll n;
    cin >> n;
    vec<vec<ll>> neigh(n);
    for(ll i = 0; i < n-1; i++){
        ll a,b;
        cin >> a >> b;
        neigh[a].push_back(b);
        neigh[b].push_back(a);
    }
    ll k;
    cin >> k;
    vec<bool> lanterns1(n,false);
    vec<bool> lanterns2(n,false);
    for(ll i = 0; i < k; i++){
        ll x;
        cin >> x;
        lanterns1[x] = true;
    }
    for(ll i = 0; i < k; i++){
        ll x;
        cin >> x;
        lanterns2[x] = true;
    }
    vec<ll> parent(n,-2);
    parent[0] = -1;
    vec<vec<ll>> children(n);
    vec<ll> frontier = {0};
    while(!frontier.empty()){
        ll pos = frontier.back();
        frontier.pop_back();
        for(ll i = 0; i < neigh[pos].size(); i++){
            if(neigh[pos][i] == parent[pos]){
                continue;
            }
            children[pos].push_back(neigh[pos][i]);
            parent[neigh[pos][i]] = pos;
            frontier.push_back(neigh[pos][i]);
        }
    }

    vec<ll> count1(n,0);
    vec<ll> count2(n,0);
    countlanterns(count1,children,lanterns1,0);
    countlanterns(count2,children,lanterns2,0);
    vec<ll> v(n);
    for(ll i = 0; i < n; i++){
        v[i] = count1[i] - count2[i];
    }

    vec<pair<pll,ll>> solution;
    f(0,solution,children,parent,v, lanterns2);

    cout << solution.size() << "\n";
    for(ll i = 0; i < solution.size(); i++){
        cout << solution[i].first.first << " " << solution[i].first.second << " " << solution[i].second << "\n";
    }

}

int main(){
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);

    ll t = 1;//cin>>t;
    while(t--)solve();
}