#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t = 1;
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> t;
  while (t--) {
    long long int start = 0, end = 0, n, m, x = 0, y = 0, index = 0;
    cin >> n;
    long int arr[n];
    unordered_map<long int, bool> mp;
    for (long int i = 1; i <= 2 * n; i++) mp[i] = true;
    for (long int i = 0; i < n; i++) {
      cin >> arr[i];
      mp[arr[i]] = false;
    }
    vector<long int> v;
    for (long int i = 0; i < n; i++) {
      v.push_back(arr[i]);
      start = 0;
      for (long int j = arr[i] + 1; j <= 2 * n; j++) {
        if (mp[j]) {
          start = 1;
          mp[j] = false;
          v.push_back(j);
          break;
        }
      }
      if (start == 0) {
        end = 1;
        cout << -1 << '\n';
        break;
      }
    }
    if (end == 0) {
      for (auto it : v) cout << it << " ";
      cout << '\n';
    }
  }
}
