#include <bits/stdc++.h>
using namespace std;
int arr[1005];
int counter[1005];
int main() {
  int tc;
  cin >> tc;
  while (tc--) {
    memset(arr, 0, 1005);
    memset(counter, 0, 1005);
    int flag = 0;
    vector<int> v;
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
      cin >> arr[i];
      counter[arr[i]]++;
    }
    int lim = 2 * n;
    for (int i = 0; i < n; i++) {
      v.push_back(arr[i]);
      for (int j = arr[i] + 1;; j++) {
        if (j > lim) {
          flag = 1;
          break;
        }
        if (!counter[j]) {
          counter[j]++;
          v.push_back(j);
          break;
        }
      }
    }
    if (flag == 1)
      cout << "-1" << endl;
    else {
      for (auto it = v.begin(); it != v.end(); ++it) cout << *it << " ";
      cout << endl;
    }
  }
}
