#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  int n;
  int in;
  bool ispossible;
  bool ischanged;
  while (t--) {
    ispossible = true;
    map<int, bool> isused;
    vector<int> a;
    vector<int> b;
    cin >> n;
    for (int i = 0; i < n; i++) {
      cin >> in;
      a.push_back(in);
      isused[in] = true;
    }
    for (int i = 0; i < n; i++) {
      ischanged = false;
      for (int j = a[i] + 1; j <= 2 * n; j++) {
        if (!isused[j]) {
          b.push_back(j);
          isused[j] = true;
          ischanged = true;
          break;
        }
      }
      if (!ischanged) {
        ispossible = false;
        break;
      }
    }
    if (!ispossible) {
      cout << -1 << endl;
    } else {
      for (int i = 0; i < n; i++) {
        cout << a[i] << ' ';
        cout << b[i] << ' ';
      }
      cout << endl;
    }
  }
}
