B.cpp

/*
    Author: Zeno_orz
*/

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

#define FAST ios::sync_with_stdio(0); \
             cout.tie(0); \
             cin.tie(0);   
#define ll long long
#define mp make_pair
#define pb push_back
#define mod 1000000007
#define el "\n"
#define len(x) x.size()
#define ste(v) v.begin(), v.end()
#define stea(arr, n) arr, arr+n
#define vll  vector<ll>
#define vpll vector<pair<ll, ll>>
#define vc   vector<char> 
#define mll  map<ll, ll>
#define sll  set<ll>


/*----------------Functions---------------*/
void primeSieve(vector<bool> &prime) {
    for(ll i=0;i<prime.size();i++) prime[i] = 1;
    for (ll i=2;i*i<=prime.size();i++) {
        if(prime[i]) {
            for(ll j=i*i;j<=prime.size();j+=i) {
                prime[j] = 0;
            }
        }
    }
}

/*----------------Functions---------------*/


void solve(){
    // Solve here
	string a, b;
	cin>>a>>b;
	// int n=0, m=0;
	bool flag = false;
	string z = a, y = b;
	int m = a.length();
	int n = b.length();
	int x = (m*n)/(__gcd(m,n));
	while(a.length()<x) {
		a+=z;
	}

	while(b.length()<x) {
		b+=y;
	}
	// cout<<flag<<endl;
	if(a==b) cout<<a<<endl;
	else cout<<-1<<endl;
    
}

int32_t main() {

    #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    #endif
    FAST
    int t;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}