#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t, n, last;
  cin >> t;
  bool can;
  for (int u = 0; u < t; ++u) {
    cin >> n;
    vector<int> a(2 * n + 1, 0);
    vector<int> c(2 * n + 1, 0);
    last = 1;
    vector<pair<int, int>> b(n);
    for (int i = 0; i < n; ++i) {
      cin >> b[i].first;
      ++c[b[i].first];
      b[i].second = i + 1;
    }
    can = true;
    for (int i = 0; i < n && can; ++i) {
      last = 1;
      while (can && (c[last] > 0 || b[i].first > last)) {
        ++last;
        if (last > 2 * n) can = false;
      }
      a[b[i].second * 2 - 1] = b[i].first;
      a[b[i].second * 2] = last;
      c[last] = 1;
    }
    if (can) {
      for (int i = 1; i <= 2 * n; ++i) {
        cout << a[i] << " ";
      }
    } else {
      cout << -1;
    }
    cout << '\n';
  }
  return 0;
}
