/******************************************************
| '_ \ / _` |/ __| '_ ` _ \ / _` | '_ \
| |_) | (_| | (__| | | | | | (_| | | | |
| .__/ \__,_|\___|_| |_| |_|\__,_|_| |_|
|_|
__| |____________________________________________
,--. ,--. ,--. ,--.
|oo | _ \ `. | oo | | oo|
o o|~~ |(_) / ; | ~~ | | ~~|o o o o o
|/\/\| '._,' |/\/\| |/\/\|
__________________ ____________________________
******************************************************/
#include <bits/stdc++.h>
//#include "bigint.h"
#define db(x) cerr << #x << ": " << x << endl
#define print cerr << "Ah shit, here we go agian" << endl
#define ll long long int
#define vii vector<int>
#define pii pair<int ,int>
#define vpi vector< pii >
#define ff first
#define ss second
#define mp make_pair
#define mod 1000000007
using namespace std;
const int maxn = 1e5 + 100, lg = 30;
int n ,m ,k, godfather;
vii adj[maxn];
int par[lg][maxn], h[maxn];
map<int ,int> mapi;
map<pii, bool> e;
vii ver;
map<int, pii> edge;
void dfs(int v, int mpar){
par[0][v] = mpar;
for(int i = 1 ; i < lg; i++){
par[i][v] = par[i - 1][par[i - 1][v]];
}
for(auto u : adj[v]){
if(u != mpar){
h[u] = h[v] + 1;
dfs(u ,v);
}
}
}
int lca (int u, int v){
if (h[u] < h[v])
swap(u, v);
for(int i = lg - 1; i >= 0 ;i--){
if(h[par[i][u]] >= h[v]){
u = par[i][u];
}
}
if (u == v)
return u;
for(int i = lg - 1; i >= 0 ;i--){
if(par[i][u] != par[i][v]){
u = par[i][u] , v= par[i][v];
}
}
return par[0][u];
}
void find_par(int v){
if(v == godfather){
return;
}
e[{v ,par[0][v]}] = true;
e[{par[0][v], v}] = true;
find_par(par[0][v]);
}
void solve(){
cin >> n >> m >> k;
for(int i = 0 ;i < n - 1; i++){
int x ,y;
cin >> x >> y;
adj[x].push_back(y);
adj[y].push_back(x);
edge[i] = {x ,y};
}
for(int i = 0 ; i < m; i++){
int x;
cin >> x;
while(x--){
int a;
cin >> a;
mapi[a]++;
}
}
for(int i = 1 ; i <= n; i++){
if(mapi[i] >= k){
ver.push_back(i);
}
}
h[1] = 1;
dfs(1 ,0);
godfather = lca(ver[0], ver[1]);
for(int i = 2; i < ver.size(); i++){
godfather = lca(godfather, ver[i]);
}
for(int i = 0 ;i < ver.size(); i++){
find_par(ver[i]);
}
int cnt= 0;
cout << ver.size() << endl;
for(int i = 0 ;i < n; i++){
if(e[edge[i]] == true){
cout << edge[i].ff << ' ' << edge[i].ss << endl;
}
}
}
signed main(){
ios_base::sync_with_stdio(0), cin.tie(0) ,cout.tie(0);
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
int t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}
