#include <bits/stdc++.h>
using namespace std;
const int N = 410;
int b[N];
int a[N];
int t, n;
bool used[N];
int find(int x) {
  for (int i = x + 1; i <= 2 * n; i++) {
    if (!used[i]) {
      return i;
    }
  }
  return -1;
}
int main() {
  ios::sync_with_stdio(false);
  cin >> t;
  while (t--) {
    memset(used, 0, sizeof(used));
    cin >> n;
    for (int i = 1; i <= n; i++) {
      cin >> b[i];
      used[b[i]] = 1;
    }
    bool noans = 0;
    for (int i = 1; i <= n; i++) {
      int f = find(b[i]);
      if (f == -1) {
        noans = 1;
        cout << -1 << endl;
        break;
      } else {
        a[2 * i - 1] = b[i];
        a[2 * i] = f;
        used[f] = 1;
      }
    }
    if (!noans) {
      for (int i = 1; i <= 2 * n; i++) {
        cout << a[i] << " ";
      }
      cout << endl;
    }
  }
  return 0;
}
