#include <bits/stdc++.h>
using namespace std;
int main() {
  int test;
  cin >> test;
  while (test--) {
    int n;
    cin >> n;
    int a[n + 5];
    int v[2 * n + 10], u[2 * n + 10];
    for (int i = 1; i <= 2 * n; i++) {
      v[i] = i;
      u[i] = i;
    }
    int j = 1;
    for (int i = 1; i <= n; i++) {
      cin >> a[i];
      v[a[i]] = 0;
      u[a[i]] = 0;
    }
    int s = 0;
    for (int i = 1; i <= n; i++) {
      for (int j = a[i]; j <= 2 * n; j++) {
        if (v[j] > a[i]) {
          s++;
          v[j] = 0;
          break;
        }
      }
    }
    if (s != n)
      cout << "-1";
    else {
      for (int i = 1; i <= n; i++) {
        for (int j = a[i]; j <= 2 * n; j++) {
          if (u[j] > a[i]) {
            cout << a[i] << " " << u[j] << " ";
            u[j] = 0;
            break;
          }
        }
      }
    }
    cout << endl;
  }
  return 0;
}
