#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  auto solve = []() {
    int n;
    cin >> n;
    vector<pair<int, int>> a(n);
    for (int i = 0; i < n; i++) {
      cin >> a[i].first;
      a[i].first--;
    }
    vector<int> ans(n + n);
    vector<int> used(n + n);
    for (int i = 0; i < n; i++) {
      ans[i * 2] = a[i].first;
      a[i].second = i * 2;
      used[a[i].first] = 1;
    }
    for (int i = 1; i < n + n; i += 2) {
      int x = ans[i - 1];
      int j;
      for (j = x + 1; j < n + n && used[j]; j++)
        ;
      if (j == n + n) {
        cout << -1 << '\n';
        return 0;
      }
      used[j] = 1;
      ans[i] = j;
    }
    for (int i = 0; i < n + n; i++) {
      if (i > 0) cout << " ";
      cout << ans[i] + 1;
    }
    cout << '\n';
  };
  while (t--) solve();
  return 0;
}
