#include <bits/stdc++.h>
using namespace std;
int tab[205];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> V;
    for (int i = 0; i < n; i++) {
      int x;
      cin >> x;
      tab[x] = 1;
      V.push_back(x);
    }
    vector<int> V2;
    bool b = 1;
    for (int i : V) {
      b = 0;
      for (int j = i + 1; j <= 2 * n; j++) {
        if (tab[j] == 0) {
          tab[j] = 1;
          b = 1;
          V2.push_back(j);
          break;
        }
      }
      if (!b) {
        break;
      }
    }
    if (!b) {
      cout << "-1\n";
    } else {
      for (int i = 0; i < n; i++) {
        cout << min(V[i], V2[i]) << " " << max(V[i], V2[i]) << " ";
      }
      cout << "\n";
    }
    for (int i = 0; i <= 2 * n; i++) {
      tab[i] = 0;
    }
  }
}
