#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, j, k, n, t, c;
  cin >> t;
  for (; t > 0; t--) {
    c = 1;
    cin >> n;
    int a[2 * n];
    bool x[2 * n + 1];
    memset(x, 0, sizeof(x));
    j = 1;
    for (i = 0; i < n; i++) {
      cin >> k;
      a[2 * i] = k;
      x[k] = 1;
    }
    for (i = 0; i < n; i++) {
      j = a[2 * i];
      j++;
      for (; x[j] == 1 && j <= 2 * n; j++)
        ;
      if (j <= 2 * n) {
        a[2 * i + 1] = j;
        x[j] = 1;
      } else
        break;
    }
    if (i == n)
      for (i = 0; i < n; i++) cout << a[2 * i] << " " << a[2 * i + 1] << " ";
    else
      cout << -1;
    cout << endl;
  }
}
