#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e16;
const long long N = 1e5 + 1;
const long long mod = 1e9 + 7;
void solve() {
  long long n;
  cin >> n;
  long long b[n + 1];
  for (long long i = 1; i <= n; i++) {
    cin >> b[i];
  }
  deque<long long> ans(2 * n + 1), rem;
  for (long long i = 1; i <= 2 * n; i++) {
    rem.push_back(i);
  }
  for (long long i = 1; i <= n; i++) {
    auto it = find(rem.begin(), rem.end(), b[i]);
    if (it != rem.end()) {
      rem.erase(it);
    }
  }
  for (long long i = 1; i <= n; i++) {
    ans[2 * i - 1] = b[i];
    auto it = upper_bound(rem.begin(), rem.end(), b[i]);
    if (it == rem.end()) {
      cout << -1 << "\n";
      return;
    }
    ans[2 * i] = *it;
    rem.erase(it);
  }
  ans.pop_front();
  for (auto x : ans) {
    cout << x << " ";
  }
  cout << "\n";
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  cin >> t;
  while (t--) solve();
  return 0;
}
