#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int main() {
  int T;
  cin >> T;
  while (T--) {
    int n;
    cin >> n;
    vector<int> a(n), ans(2 * n), used(2 * n + 5);
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      used[a[i]] = 1;
      ans[i * 2] = a[i];
    }
    for (int i = 1; i < 2 * n; i += 2) {
      for (int j = ans[i - 1] + 1; j <= 2 * n; j++)
        if (!used[j]) {
          ans[i] = j;
          used[j] = 1;
          break;
        }
    }
    bool bad = false;
    for (int i = 0; i < 2 * n; i++)
      if (ans[i] == 0) {
        cout << "-1\n";
        bad = true;
        break;
      }
    if (bad) continue;
    for (int i = 0; i < 2 * n; i++) cout << ans[i] << ' ';
    cout << '\n';
  }
}
