#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> b(n);
    vector<int> ans;
    map<int, bool> m;
    for (int i = 0; i < n; i++) {
      cin >> b[i];
      m[b[i]] = 1;
    }
    int i;
    for (i = 0; i < n; i++) {
      ans.push_back(b[i]);
      int temp = b[i] + 1;
      while (m[temp]) {
        temp++;
        if (temp > 2 * n) break;
      }
      if (temp > 2 * n) break;
      m[temp] = 1;
      ans.push_back(temp);
    }
    if (i != n)
      cout << -1 << endl;
    else {
      for (auto j : ans) cout << j << " ";
      cout << endl;
    }
  }
}
