#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
const long long inf = 0x3f3f3f3f;
const long long nax = 0;
void solve() {
  long long n;
  vector<long long> b(210, 0), arr(105);
  vector<bool> vis(210, 0);
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> arr[i];
    vis[arr[i]] = 1;
  }
  for (int i = 1; i <= n; ++i) {
    b[2 * i - 1] = arr[i];
    int angka = arr[i] + 1;
    while (vis[angka] && angka <= 2 * n) {
      if (angka == 2 * n) {
        angka = -1;
        break;
      }
      angka++;
    }
    if (angka == -1 || angka > n * 2) {
      cout << "-1" << '\n';
      return;
    }
    vis[angka] = 1;
    b[2 * i] = angka;
  }
  for (int i = 1; i <= 2 * n; ++i) {
    cout << b[i] << ' ';
  }
  cout << '\n';
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie();
  cout.tie();
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}
