#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
int b[100 + 5], a[200 + 10];
bool used[200 + 10];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int t, n;
  cin >> t;
  while (t--) {
    cin >> n;
    memset(a, -1, sizeof a);
    memset(used, false, sizeof used);
    memset(b, -1, sizeof b);
    bool flag = false;
    for (int i = 0; i < n; i++) {
      cin >> b[i];
    }
    for (int i = 0; i < 2 * n; i += 2) {
      a[i] = b[i / 2];
      used[b[i / 2]] = true;
    }
    for (int i = 1; i < 2 * n; i += 2) {
      flag = false;
      for (int j = a[i - 1] + 1; j <= 2 * n; j++) {
        if (!used[j]) {
          a[i] = j;
          used[j] = true;
          flag = true;
          break;
        }
      }
      if (!flag) {
        cout << -1 << endl;
        break;
      }
    }
    if (flag) {
      for (int i = 0; i < 2 * n; i++) {
        cout << a[i] << " ";
      }
      cout << endl;
    }
  }
  return 0;
}
