#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    long long b[n];
    for (long long i = 0; i < n; i++) cin >> b[i];
    bool c[2 * n + 1];
    memset(c, true, 2 * n + 1);
    long long a[2 * n];
    memset(a, -1, 2 * n);
    for (long long i = 0; i < n; i++) {
      a[2 * i] = b[i];
      c[b[i]] = false;
    }
    bool T = true;
    for (long long i = 1; i < 2 * n; i += 2) {
      long long j = a[i - 1];
      while (c[j] == false && j <= 2 * n) {
        j++;
      }
      if (j > 2 * n) {
        T = false;
        break;
      }
      a[i] = j;
      c[j] = false;
    }
    if (!T) {
      cout << -1 << endl;
      continue;
    }
    for (long long i = 0; i < 2 * n; i++) {
      cout << a[i] << " ";
    }
    cout << endl;
  }
}
