#include <bits/stdc++.h>
using namespace std;
#define For(Ti,Ta,Tb) for(auto Ti=(Ta);Ti<=(Tb);++Ti)
#define Dec(Ti,Ta,Tb) for(auto Ti=(Ta);Ti>=(Tb);--Ti)
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define range(Tx) begin(Tx),end(Tx)
using ll=long long;
const int N=1e6+5,B=200;
int n,q,id[N],tot,ans[N/B][N/B];
vector<int> vec[N],occ[N];
bitset<N> bs[N/B];
int main(){
	cin.tie(nullptr)->sync_with_stdio(false);
	cin>>n>>q;
	For(i,1,n){
		int len;
		cin>>len;
		vec[i].resize(len);
		For(j,0,len-1) cin>>vec[i][j];
		sort(range(vec[i]));
		if(len>=B){
			id[i]=tot++;
			for(int x:vec[i]){
				bs[id[i]].set(x);
				occ[x].push_back(i);
			}
		}
	}
	memset(ans,-1,sizeof(ans));
	For(x,1,int(1e6)){
		for(int i:occ[x]){
			for(int j:occ[x]){
				ans[id[i]][id[j]]=x;
			}
		}
	}
	For(i,1,q){
		int x,y;
		cin>>x>>y;
		if(vec[x].size()<vec[y].size()){
			swap(x,y);
		}
		if(int(vec[y].size())>=B){
			cout<<ans[id[x]][id[y]]<<'\n';
			continue;
		}
		if(int(vec[x].size())<B){
			int ans=-1;
			for(int i=0,j=0;i<int(vec[x].size())&&j<int(vec[y].size());++i){
				while(j<int(vec[y].size())&&vec[y][j]<vec[x][i]){
					++j;
				}
				if(j<int(vec[y].size())&&vec[y][j]==vec[x][i]){
					ans=vec[x][i];
					break;
				}
			}
			cout<<ans<<'\n';
			continue;
		}
		int ans=-1;
		for(int z:vec[y]){
			if(bs[id[x]].test(z)){
				ans=z;
				break;
			}
		}
		cout<<ans<<'\n';
	}
	return 0;
}