#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<bool> a(2 * n + 1);
    vector<int> res(2 * n);
    bool good = true;
    for (int i = 0; i < n; i++) {
      int k;
      cin >> k;
      if (a[k] == false) {
        a[k] = true;
        res[2 * i] = k;
      } else {
        good = false;
        break;
      }
    }
    if (!good) {
      cout << -1 << endl;
      continue;
    }
    for (int i = 1; i < 2 * n; i += 2) {
      int ptr = -1;
      for (int j = res[i - 1] + 1; j <= 2 * n; j++) {
        if (!a[j]) {
          ptr = j;
          break;
        }
      }
      if (ptr == -1) {
        good = false;
        break;
      }
      a[ptr] = true;
      res[i] = ptr;
    }
    if (!good) {
      cout << -1 << endl;
      continue;
    }
    for (int i = 0; i < 2 * n; i++) cout << res[i] << ' ';
    cout << endl;
  }
  return 0;
}
