#include <bits/stdc++.h>
using namespace std;
long long a[250];
long long b[250];
long long c[250];
signed main() {
  long long t;
  cin >> t;
  while (t--) {
    long long f;
    cin >> f;
    memset(b, 0, sizeof(b));
    for (long long i = 1; i <= f; i++) {
      cin >> a[i];
      b[a[i]] = 1;
    }
    long long cnt = 0;
    for (long long i = 1; i <= f; i++) {
      for (long long j = a[i] + 1; j <= 2 * f; j++) {
        if (b[j] == 0) {
          b[j] = 1, c[i] = j, cnt++;
          j = 2 * f + 1;
        }
      }
    }
    if (cnt != f) {
      cout << -1 << endl;
    } else {
      for (long long i = 1; i <= f; i++) {
        cout << a[i] << " " << c[i] << " ";
      }
      cout << endl;
    }
  }
  return 0;
}
