#include <bits/stdc++.h>
using namespace std;
int i, j, n, k, t, a[240], b[105], p[240];
int main() {
  cin >> t;
  for (k = 1; k <= t; k++) {
    cin >> n;
    for (i = 0; i++ < n;) {
      cin >> b[i];
      p[b[i]] = 1;
    }
    for (i = 0; i++ < n;) {
      for (j = b[i]; p[j] && j <= 2 * n;) j++;
      if (j > 2 * n) {
        cout << -1 << endl;
        goto G;
      }
      a[2 * i - 1] = b[i];
      a[2 * i] = j;
      p[j] = 1;
    }
    for (i = 0; i++ < 2 * n;) cout << a[i] << ' ';
    cout << endl;
  G:
    for (i = 0; i++ < 2 * n;) p[i] = 0;
  }
}
