#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    long long b[n];
    unordered_map<long long, long long> mapp;
    for (long long i = 0; i < n; i++) {
      cin >> b[i];
      mapp[b[i]]++;
    }
    long long a[n];
    long long x = 0;
    long long z = 0;
    for (long long i = 0; i < n; i++) {
      bool chk = false;
      for (long long j = b[i] + 1; j <= 2 * n; j++) {
        if (mapp[j]) {
          continue;
        } else {
          chk = true;
          a[x] = j;
          mapp[a[x]]++;
          x++;
          break;
        }
      }
      if (chk == false) {
        z++;
        break;
      }
    }
    if (z) {
      cout << "-1" << '\n';
    } else {
      for (long long i = 0; i < n; i++) {
        cout << b[i] << " " << a[i] << " ";
      }
      cout << '\n';
    }
  }
}
