#include <bits/stdc++.h>
using namespace std;
const long long int inf = 1e18, N = (long long int)1e5 + 5;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  long long int i, j, k, n, m, t, p, flag, x, y, z, count, a, b, c, d;
  cin >> t;
  while (t--) {
    cin >> n >> m >> k;
    if (n % 2 == 0) {
      if (k % 2 == 0 && k <= (m / 2) * n) {
        cout << "YES\n";
        i = 0, j = 0;
        string s = "";
        for (i = 0; i < m; i++) s += '0';
        i = 0;
        vector<string> v(n, s);
        char temp = 'a';
        while (k > 0) {
          v[i][j] = temp;
          v[i][j + 1] = temp;
          i++;
          temp = 'a' + 'b' - temp;
          k--;
          if (i >= n) {
            i = 0;
            j += 2;
            if (j % 4 == 0)
              temp = 'a';
            else
              temp = 'b';
          }
        }
        for (i = 0; i < n; i++) {
          if (i % 4 == 0)
            temp = 'e';
          else
            temp = 'f';
          for (j = 0; j < m; j++) {
            if (v[i][j] == '0') {
              v[i][j] = temp;
              v[i + 1][j] = temp;
              temp = 'e' + 'f' - temp;
            }
          }
        }
        for (i = 0; i < n; i++) cout << v[i] << "\n";
      } else
        cout << "NO\n";
    } else {
      if ((k + (m / 2)) % 2 == 0 && k >= m / 2) {
        cout << "YES\n";
        string s = "";
        for (i = 0; i < m; i++) s += '0';
        vector<string> v(n, s);
        char temp = 'a';
        for (i = 0; i < m - 1; i += 2) {
          v[0][i] = temp;
          v[0][i + 1] = temp;
          if (temp == 'a')
            temp = 'b';
          else
            temp = 'a';
        }
        k -= (m / 2);
        i = 1;
        j = 0;
        temp = 'c';
        while (k > 0) {
          if (j % 4)
            temp = 'c';
          else
            temp = 'd';
          v[i][j] = temp;
          v[i][j + 1] = temp;
          if (temp == 'c')
            temp = 'd';
          else
            temp = 'c';
          v[i + 1][j] = temp;
          v[i + 1][j + 1] = temp;
          j += 2;
          k -= 2;
          if (j >= m) {
            i += 2;
            j = 0;
          }
        }
        for (i = 0; i < n; i++) {
          if (i % 4 == 1)
            temp = 'e';
          else
            temp = 'f';
          for (j = 0; j < m; j++) {
            if (v[i][j] == '0') {
              v[i][j] = temp;
              v[i + 1][j] = temp;
              temp = 'e' + 'f' - temp;
            }
          }
        }
        for (i = 0; i < n; i++) cout << v[i] << "\n";
      } else
        cout << "NO\n";
    }
  }
  return 0;
}
