#include <bits/stdc++.h>
const long long MX = 1e18, N = 1e4 + 10;
const double PI = 3.141592653589793238;
using namespace std;
long long n, m, ans[N], a[N], t;
map<int, int> mp;
int main() {
  cin >> t;
  while (t--) {
    cin >> n;
    bool yes = true;
    for (int i = 1; i <= n; ++i) {
      cin >> a[i];
      ++mp[a[i]];
    }
    for (int i = 1; i <= n; ++i) {
      bool ok = false;
      ans[i * 2 - 1] = a[i];
      for (int j = a[i] + 1; j <= n * 2; ++j) {
        if (!mp[j]) {
          ans[i * 2] = j;
          mp[j]++;
          ok = true;
          break;
        }
      }
      if (!ok) yes = false;
    }
    if (yes) {
      for (int i = 1; i <= n * 2; i++) cout << ans[i] << ' ';
    } else
      cout << -1;
    cout << '\n';
    mp.clear();
  }
  return 0;
}
