#include <bits/stdc++.h>
using namespace std;
int t, n, i, j;
int b[105];
int a[210];
bool dd[210];
long tong;
int sl;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> t;
  while (t--) {
    cin >> n;
    memset(dd, false, sizeof(dd));
    tong = 0;
    for (i = 1; i <= n; i++) {
      cin >> b[i];
      a[2 * i - 1] = b[i];
      tong += b[i];
      dd[b[i]] = true;
    }
    sl = 0;
    for (i = 2; i <= 2 * n; i += 2) {
      for (j = a[i - 1] + 1; j <= 300; j++) {
        if (dd[j] == false) {
          tong += j;
          a[i] = j;
          dd[j] = true;
          break;
        }
      }
    }
    sl = 2 * n;
    if (sl * (sl + 1) != tong * 2)
      cout << -1;
    else
      for (i = 1; i <= 2 * n; i++) cout << a[i] << ' ';
    cout << '\n';
  }
  return 0;
}
