#include <bits/stdc++.h>
int main() {
  int t;
  scanf("%d", &t);
  while (t--) {
    int n, b[100] = {0};
    bool used[201] = {false};
    scanf("%d", &n);
    for (int i = 0; i < n; i++) {
      scanf("%d", &b[i]);
      used[b[i]] = true;
    }
    bool ok = true;
    int ans[200];
    for (int i = 0; i < n; i++) {
      ans[2 * i] = b[i];
      int j = b[i] + 1;
      while (j <= 2 * n && used[j]) j++;
      if (j > 2 * n) {
        ok = false;
        break;
      }
      ans[2 * i + 1] = j;
      used[j] = true;
    }
    if (ok) {
      for (int i = 0; i < 2 * n; i++) printf("%d ", ans[i]);
      puts("");
    } else {
      puts("-1");
    }
  }
  return 0;
}
