#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long t;
  cin >> t;
  while (t--) {
    long long vis[205] = {0};
    long long n, c = 0;
    cin >> n;
    long long a[n];
    vector<long long> b;
    for (long long i = 0; i < n; i++) {
      cin >> a[i];
      vis[a[i]] = 1;
    }
    for (long long i = 0; i < n; i++) {
      b.push_back(a[i]);
      for (long long j = a[i] + 1; j <= 2 * n; j++) {
        if (!vis[j]) {
          b.push_back(j);
          vis[j] = 1;
          break;
        }
      }
    }
    if (b.size() == 2 * n) {
      for (long long i = 0; i < 2 * n; i++) cout << b[i] << " ";
    } else
      cout << "-1";
    cout << "\n";
  }
  return 0;
}
