#include <bits/stdc++.h>
using namespace std;
int main() {
  int T;
  cin >> T;
  bool used[314] = {};
  int A[210] = {};
  while (T--) {
    int N;
    cin >> N;
    for (int i = 0; i < N; i++) {
      cin >> A[i * 2];
      used[A[i * 2]] = true;
    }
    for (int i = 0; i < N; i++) {
      int j = A[i * 2] + 1;
      while (used[j]) j++;
      A[i * 2 + 1] = j;
      used[j] = true;
    }
    bool ok = true;
    for (int i = 1; i <= N * 2; i++) {
      if (!used[i]) ok = false;
    }
    if (!ok)
      cout << -1 << endl;
    else {
      for (int i = 0; i < N * 2; i++) cout << A[i] << " ";
      cout << endl;
    }
    ok = true;
    fill(used, used + 310, false);
  }
}
