#include <bits/stdc++.h>
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")

#define int long long
#define ld long double
#define vec vector
#define all(m) (m).begin(), (m).end()
#define forn(i,n) for(int i=0;i<(n);i++)

// TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
using namespace std;

typedef pair<int, int> pii;

int mod = 1e9+7;

vec<vec<int>> g;
vec<int> p;
vec<int> h;

void dfs(int v, int hh) {
    h[v] = hh;
    for (int u: g[v]) {
        if (h[u]<0) {
            p[u] = v;
            dfs(u,hh+1);
        }
    }
}

struct p3 {
    int a,b,c;
};

void solve() {
    int n;
    cin>>n;
    g.resize(n);
    forn(i,n-1) {
        int a,b;
        cin>>a>>b;
        g[a].push_back(b);
        g[b].push_back(a);
    }

    int k; cin>>k;
    vec<int> need(n);
    forn(i,k) {
        int v;
        cin>>v;
        need[v]++;
    }
    forn(i,k) {
        int v;
        cin>>v;
        need[v]--;
    }
    p.assign(n,-1);
    h.assign(n,-1);
    dfs(0,0);
    priority_queue<pii> pq;
    queue<p3> ans1;
    stack<p3> ans2;
    forn(i,n) {
        if (need[i])
            pq.push({h[i],i});
    }
    while (!pq.empty()) {
        int v = pq.top().second;
        pq.pop();
        if (!need[v])
            continue;
        if (!need[p[v]])
            pq.push({h[p[v]],p[v]});
        if (need[v]>0) {
            ans1.push({v,p[v],need[v]});
        }
        else {
            ans2.push({p[v],v,-need[v]});
        }
        need[p[v]] += need[v];
        need[v] = 0;
    }
    cout<<ans1.size()+ans2.size()<<'\n';
    while (!ans1.empty()) {
        cout<<ans1.front().a<<" "<<ans1.front().b<<" "<<ans1.front().c<<'\n';
        ans1.pop();
    }
    while (!ans2.empty()) {
        cout<<ans2.top().a<<" "<<ans2.top().b<<" "<<ans2.top().c<<'\n';
        ans2.pop();
    }
}

signed main() {

    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int tt = 1;
    // cin>>tt;
    while (tt--)
        solve();
    return 0;
}