#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n;
  cin >> n;
  vector<long long> line(n);
  for (long long& i : line) cin >> i;
  set<long long> av;
  for (long long i = 1; i <= 2 * n; i++) av.insert(i);
  for (long long i : line) av.erase(i);
  vector<long long> ans(2 * n);
  for (long long i = 0; i < n; i++) {
    ans[2 * i] = line[i];
    auto it = av.lower_bound(line[i]);
    if (it == av.end()) {
      cout << -1 << endl;
      return;
    }
    ans[2 * i + 1] = *it;
    av.erase(it);
  }
  for (long long i : ans) cout << i << " ";
  cout << endl;
}
signed main() {
  long long q = 1;
  cin >> q;
  while (q--) {
    solve();
  }
  return 0;
}
