#include <bits/stdc++.h>
using namespace std;
using ll = long long;
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> b(n);
    vector<int> a(2 * n);
    vector<char> used(2 * n);
    for (int i = 0; i < n; ++i) {
      cin >> b[i];
      --b[i];
      used[b[i]] = true;
      a[2 * i] = b[i];
    }
    bool good = true;
    for (int i = 0; i < n; ++i) {
      int j = b[i] + 1;
      for (; j < 2 * n; ++j) {
        if (!used[j]) {
          break;
        }
      }
      if (j == 2 * n) {
        good = false;
        break;
      }
      used[j] = true;
      a[2 * i + 1] = j;
    }
    if (good) {
      for (auto e : a) cout << e + 1 << " ";
    } else {
      cout << -1;
    }
    cout << "\n";
  }
}
