#include <bits/stdc++.h>
using namespace std;
signed main() {
  long long int t = 1;
  cin >> t;
  while (t--) {
    long long int n;
    cin >> n;
    vector<long long int> b(n);
    for (auto &x : b) cin >> x;
    vector<bool> use(2 * n + 1, 0);
    vector<long long int> a(2 * n + 1, 0);
    for (auto x : b) use[x] = 1;
    bool ok = 1;
    for (long long int i = 1; i <= n; i++) {
      a[2 * i - 1] = b[i - 1];
      use[b[i - 1]] = 1;
      bool f = 0;
      for (long long int j = b[i - 1] + 1; j <= 2 * n; j++) {
        if (use[j] == 0) {
          a[2 * i] = j;
          use[j] = 1;
          f = 1;
          break;
        }
      }
      if (!f) {
        ok = 0;
        break;
      }
    }
    if (!ok)
      cout << -1 << endl;
    else {
      for (long long int i = 1; i <= 2 * n; i++) cout << a[i] << " ";
      cout << endl;
    }
  }
}
