#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, t;
  cin >> t;
  while (t--) {
    cin >> n;
    int b[n + 1], a[2 * n + 1];
    bool marked[2 * n + 1];
    memset(a, -1, sizeof a);
    memset(marked, true, sizeof marked);
    bool yes = true;
    for (int i = 1; i <= n; i++) {
      cin >> b[i];
      if (marked[b[i]] == false) yes = false;
      marked[b[i]] = false;
      a[2 * i - 1] = b[i];
    }
    for (int i = 1; i < 2 * n + 1; i++) {
      if (a[i] == -1) {
        bool got = false;
        int j = a[i - 1] + 1;
        while (j < 2 * n + 1 && marked[j] == false) {
          j++;
        }
        if (j < 2 * n + 1 && marked[j]) {
          marked[j] = false;
          a[i] = j;
          got = true;
        }
        if (!got) yes = false;
      }
    }
    if (!yes)
      cout << -1 << '\n';
    else {
      for (int i = 1; i < 2 * n + 1; i++) {
        cout << a[i] << ' ';
      }
      cout << '\n';
    }
  }
  return 0;
}
