#include <bits/stdc++.h>
using namespace std;
int b[100];
int a[201];
int main(void) {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    set<int> left;
    for (int i = 1; i <= (2 * n); i++) {
      left.insert(i);
    }
    for (int i = 0; i < n; i++) {
      cin >> b[i];
      left.erase(b[i]);
    }
    int can = 1;
    for (int i = 0; i < n; i++) {
      a[2 * i] = b[i];
      auto it = left.upper_bound(b[i]);
      if (it == left.end()) {
        can = 0;
        break;
      }
      a[2 * i + 1] = *it;
      left.erase(it);
    }
    if (!can)
      cout << "-1\n";
    else {
      for (int i = 0; i < 2 * n; i++) {
        cout << a[i] << ' ';
      }
      cout << '\n';
    }
  }
  return 0;
}
