// #include <format>
#include <climits>
#include <iostream>
#include <fstream>
#include <assert.h>
#include <algorithm>
#include <vector>
#include <set>
#include <string>
#include <queue>
#include <map>

# define pb push_back 
#define pii pair<int, int>
#define mp make_pair
# define ll long long int

using namespace std;
  
FILE *fp;
ofstream outfile;

const int maxt = 100, maxsumn = 1000;
char seq[4] = {'A', 'T', 'C', 'G'};
int main()
{   
    
    int t; cin >> t;
    int sumn = 0;
    while(t--){
        int n; cin >> n;
        assert(n % 2 == 0);
        sumn += n;
        string s; cin >> s;
        for(char c : s)assert(c == '0' || c == '1');
        for(int i = 0; i < n; i += 2){
            cout << seq[(s[i] - '0') * 2 + (s[i + 1] - '0')];
        }
        cout << endl;
    }
    assert(sumn <= maxsumn);
    // assert(getchar()==-1);
}