#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const long long inf = 1000000000;
const long long N = 2 * (1e2) + 5;
long long ar[N];
long long ans[N];
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long t = 1;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<long long> done(2 * n + 1, 0);
    for (long long i = 1; i <= n; ++i) {
      cin >> ar[i];
      done[ar[i]] = 1;
    }
    long long d = 1;
    for (long long i = 1; i <= n; ++i) {
      long long x = ar[i];
      long long y = 0;
      for (long long val = x + 1; val <= 2 * n; ++val) {
        if (!done[val]) {
          y = val;
          done[val] = 1;
          break;
        }
      }
      if (!y) {
        d = 0;
        break;
      }
      ans[i] = y;
    }
    if (!d)
      cout << -1 << "\n";
    else {
      for (long long i = 1; i <= n; ++i) {
        cout << ar[i] << " " << ans[i] << " ";
      }
      cout << "\n";
    }
  }
}
