#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int b[n];
    int ans[2 * n];
    for (long long i = 0; i < n; i++) cin >> b[i];
    set<int> a;
    for (long long i = 0; i < 2 * n; i++) a.insert(i + 1);
    for (long long i = 0; i < n; i++) {
      ans[2 * i] = b[i];
      a.erase(b[i]);
    }
    bool poss = true;
    for (long long i = 0; i < n; i++) {
      set<int>::iterator up = upper_bound(a.begin(), a.end(), b[i]);
      if (up != a.end()) {
        ans[2 * i + 1] = *up;
        a.erase(up);
      } else {
        cout << -1 << '\n';
        poss = false;
        break;
      }
    }
    if (poss) {
      for (long long i = 0; i < 2 * n - 1; i++) cout << ans[i] << ' ';
      cout << ans[2 * n - 1] << '\n';
    }
  }
  return 0;
}
