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#pragma GCC optimize("O2,no-stack-protector,unroll-loops")
#define ll long long
#define pb push_back
#define ipar(arr, n) vector<ll> arr(n); for(int i=0;i<n;i++) cin>>arr[i];
#include <cmath>
#include <bits/stdc++.h>
#define pii pair<int, int>;
#define pll pair<ll, ll>;
using namespace std;


void solve(){
    ll n;cin>>n;
    vector<vector<char>> arr(n);
    for(int i=0;i<n;i++){
        string s;cin>>s;
        vector<char>g(s.begin(),s.end());
        arr[i]=g;
    }
    
    vector<char>res(n);
    ll ind=0;
    for(int i=0;i<n;i++){
        if(arr[i][ind]=='0') res[i]='1';
        else res[i]='0';
        ind++;
    }
    string re(res.begin(),res.end());
    cout<<re<<"\n";
    
}


signed main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    int t;
	cin>>t;
	while(t--) solve();
}