#include <bits/stdc++.h>
using namespace std;
const int N = 105;
long long n, m, k, xx, t, cnt, cnt1, bb[N][N];
char ans[N][N], ans1[N][N];
void go(int i, int j) {
  if (k > 0) {
    if (bb[i][j] == 1) {
      ans[i][j] = 'a';
      ans[i][j + 1] = 'a';
      ans[i + 1][j] = 'b';
      ans[i + 1][j + 1] = 'b';
    } else {
      ans[i][j] = 'c';
      ans[i][j + 1] = 'c';
      ans[i + 1][j] = 'd';
      ans[i + 1][j + 1] = 'd';
    }
    k -= 2;
  } else {
    if (bb[i][j] == 1) {
      ans[i][j] = 'a';
      ans[i + 1][j] = 'a';
      ans[i][j + 1] = 'b';
      ans[i + 1][j + 1] = 'b';
    } else {
      ans[i][j] = 'c';
      ans[i + 1][j] = 'c';
      ans[i][j + 1] = 'd';
      ans[i + 1][j + 1] = 'd';
    }
  }
}
int main() {
  cin >> t;
  while (t--) {
    cin >> n >> m >> k;
    if (n % 2 == 0 && m % 2 == 0) {
      if (k % 2 == 0) {
        cout << "YES" << endl;
        cnt1 = 0;
        for (int i = 1; i <= n; i += 2) {
          cnt1++;
          cnt = cnt1 % 2;
          for (int j = 1; j <= m; j += 2) {
            bb[i][j] = bb[i][j + 1] = cnt;
            bb[i + 1][j] = bb[i + 1][j + 1] = cnt;
            cnt++;
            cnt %= 2;
          }
        }
        for (int i = 1; i <= n; i += 2) {
          for (int j = 1; j <= m; j += 2) {
            go(i, j);
          }
        }
        for (int i = 1; i <= n; i++) {
          for (int j = 1; j <= m; j++) {
            cout << ans[i][j] << "";
          }
          cout << endl;
        }
        continue;
      }
      cout << "NO" << endl;
      continue;
    }
    long long fff = 0;
    if (n % 2 == 1) swap(n, m), k = (n * m) / 2 - k, fff = 1;
    if (k % 2 == 1) {
      cout << "NO" << endl;
      continue;
    }
    xx = n * m - n;
    xx /= 2;
    if (k > xx) {
      cout << "NO" << endl;
      continue;
    }
    for (int i = 1; i <= n; i += 2) {
      cnt1++;
      cnt = cnt1 % 2;
      for (int j = 1; j <= m; j += 2) {
        bb[i][j] = bb[i][j + 1] = cnt;
        bb[i + 1][j] = bb[i + 1][j + 1] = cnt;
        cnt++;
        cnt %= 2;
      }
    }
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= m; j++) {
      }
    }
    for (int i = 1; i <= n; i += 2) {
      for (int j = 1; j < m; j += 2) {
        go(i, j);
      }
    }
    for (int i = 1; i <= n; i++) {
      if (bb[i][m] == 1)
        ans[i][m] = 'a';
      else
        ans[i][m] = 'c';
    }
    cout << "YES" << endl;
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= m; j++) {
        if (fff) ans1[j][i] = ans[i][j];
      }
    }
    if (fff) swap(n, m);
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= m; j++) {
        if (fff)
          cout << ans1[i][j] << "";
        else
          cout << ans[i][j] << "";
      }
      cout << endl;
    }
  }
}
