#include <bits/stdc++.h>
using namespace std;
long long int mod = 1000000007;
long long int power(long long int a, long long int c) {
  if (c == 0) return 1;
  if (c % 2 == 0) {
    long long int m = power(a, c / 2);
    return (m * m) % mod;
  }
  return (a * power(a, c - 1)) % mod;
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long int t;
  cin >> t;
  for (long long int w1 = 0; w1 < t; w1++) {
    long long int n;
    cin >> n;
    long long int a[n];
    map<long long int, long long int> m;
    for (long long int i = 0; i < n; i++) {
      cin >> a[i];
      m[a[i]]++;
    }
    vector<long long int> v;
    for (long long int i = 0; i < n; i++) {
      for (long long int j = a[i]; j <= 2 * n; j++) {
        if (m[j] == 0) {
          v.push_back(a[i]);
          v.push_back(j);
          m[j]++;
          break;
        }
      }
    }
    if (v.size() != 2 * n)
      cout << -1 << endl;
    else {
      for (long long int i = 0; i < v.size(); i++) cout << v[i] << " ";
      cout << endl;
    }
  }
  return 0;
}
