#include <algorithm>

#include <cassert>

#include <cmath>

#include <cstdio>

#include <cstring>

#include <iostream>

#include <map>

#include <queue>

#include <set>

#include <string>

#include <tuple>

#define LOCAL_DEBUG

using namespace std;

typedef pair<int, int> MyPair;

int cnt[][];

int main() {

#ifdef LOCAL_DEBUG

    freopen("C:\\Users\\Iris\\source\\repos\\ACM\\ACM\\input.txt", "r", stdin);

    //freopen("C:\\Users\\Iris\\source\\repos\\ACM\\ACM\\output.txt", "w", stdout);

#endif // LOCAL_DEBUG

    int T;

    int m, n;

    cin >> T;

    for (int ti = ;cin>>m>>n; ti++) {

        string tmp;

        memset(cnt, , sizeof cnt);

        for (int i = ; i < m; i++) {

            cin >> tmp;

            for (int j = ; j < n; j++) {

                cnt[j][tmp[j]]++;

            }

        }

        int ans = ;

        for (int j = ; j < n; j++) {

            char anschar = 'A';

            for (char ch : {'A', 'C', 'G', 'T'}) {

                if (cnt[j][ch] > cnt[j][anschar]) {

                    anschar = ch;

                }

            }

            putchar(anschar);

            ans += m - cnt[j][anschar];

        }

        putchar('\n');

        printf("%d\n", ans);

    }

    return ;

}