#include <bits/stdc++.h>
using namespace std;
const int siz = 1e5 + 7;
const int siz2 = 2e5 + 7;
int t, n;
int a[222];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> t;
A:
  while (t--) {
    cin >> n;
    map<int, int> mp;
    vector<int> Ans;
    for (int i = 0; i < n; ++i) {
      cin >> a[i];
      mp[a[i]]++;
    }
    if (n > 1) {
      for (int i = 0; i < n; ++i) {
        for (int j = a[i]; j <= 2 * n; ++j) {
          if (!mp[j]) {
            mp[j]++;
            Ans.push_back(a[i]);
            Ans.push_back(j);
            break;
          }
        }
      }
      if (Ans.size() != 2 * n) {
        cout << -1 << endl;
        goto A;
      }
    } else {
      if (a[0] == 1) {
        cout << 1 << " " << 2 << endl;
        goto A;
      } else {
        cout << -1 << endl;
        goto A;
      }
    }
    for (auto it : Ans) cout << it << " ";
    cout << endl;
  }
  return 0;
}
