#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 ar2[N];
long long ar3[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 j = 1;
    for (long long i = 1; i <= 2 * n; ++i) {
      if (!done[i]) {
        ar2[j++] = i;
      }
    }
    long long d = 1;
    for (long long i = 1; i <= n; ++i) {
      long long b = 0;
      long long j = lower_bound(ar2 + 1, ar2 + 1 + n, ar[i] + 1) - ar2;
      while (j <= n) {
        if (!done[ar2[j]]) {
          done[ar2[j]] = 1;
          ar3[i] = ar2[j];
          b = 1;
          break;
        }
        j++;
      }
      if (!b) {
        d = 0;
        break;
      }
    }
    if (!d)
      cout << -1 << "\n";
    else {
      for (long long i = 1; i <= n; ++i) {
        cout << ar[i] << " " << ar3[i] << " ";
      }
      cout << "\n";
    }
  }
}
