#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> a(n), b(2 * n);
    for (int &i : a) cin >> i;
    set<int> s;
    for (int i = 1; i <= 2 * n; i++) s.insert(i);
    for (int i = 0; i < n; i++) {
      b[2 * i] = a[i];
      auto it = s.find(a[i]);
      s.erase(it);
    }
    for (int i = 0; i < n; i++) {
      auto it = s.upper_bound(a[i]);
      if (it != s.end()) {
        b[2 * i + 1] = *it;
        s.erase(it);
      }
    }
    if (s.size())
      cout << -1 << endl;
    else {
      for (int i = 0; i < n; i++)
        cout << b[2 * i] << " " << b[2 * i + 1] << " ";
      cout << endl;
    }
  }
}
