#include <iostream>using namespace std;#ifdef WIN32#define for if (0); else for#endifchar mat[50][21];char output[27];int index;int sign[26];int main(){int kase;cin >> kase;for (int t = 0; t < kase; t ++){if (t) cout << endl;int n;cin >> n;for (int i = 0; i < 26; i ++) sign[i] = 1;for (int i = 0; i < n; i ++){cin >> mat[i];for (int j = 0; j < 20; j ++){if (mat[i][j] != '.') sign[mat[i][j] - 'A'] = 0;}}int total = 0;for (int i = 0; i < 26; i ++){if (sign[i] == 0) total ++;}index = 0;while (1) {again:for (int i = 0; i < 26; i ++){if (sign[i] == 1) continue;int possible = 1;for (int j = 0; j < n - 1; j ++){for (int s = 0; s < 20; s ++){if (mat[j][s] == i + 'A'){if (mat[j + 1][s] != i + 'A' && mat[j + 1][s] != '.'){possible = 0;break;}}}if (possible == 0) break;}if (possible){for (int j = 0; j < n; j ++){for (int s = 0; s < 20; s ++){if (mat[j][s] == i + 'A') mat[j][s] = '.';}}sign[i] = 1;total --;output[index ++] = i + 'A';if (total == 0) goto out;goto again;}}}out:for(int i = 0; i < index; i ++) cout << output[i];cout << endl;}return 0;}
