#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int a[n + 1];
    int b[2 * n + 1];
    int temp[2 * n + 1];
    for (int i = 1; i <= 2 * n; i++) temp[i] = 0;
    bool con1 = false, con2 = false;
    for (int i = 1; i <= n; i++) {
      cin >> a[i];
      if (a[i] == 1) con1 = true;
      if (a[i] == 2 * n) con2 = true;
      temp[a[i]] = 1;
    }
    if (con1 == false or con2 == true)
      cout << "-1" << endl;
    else {
      int check = 0;
      for (int i = 1; i <= n; i++) {
        b[2 * i - 1] = a[i];
        int j;
        for (j = a[i] + 1; j <= 2 * n; j++) {
          if (temp[j] == 0) {
            temp[j] = 1;
            b[2 * i] = j;
            break;
          }
        }
        if (j == 2 * n + 1) {
          check = -1;
        }
      }
      if (check != -1) {
        for (int i = 1; i <= 2 * n; i++) cout << b[i] << " ";
        cout << endl;
      } else
        cout << "-1" << endl;
    }
  }
  return 0;
}
