#include <bits/stdc++.h>
using namespace std;
long long int n, m;
long long int arr[3000000];
long long int brr[3000000];
long long int an[3000000];
array<long long int, 2> dp[3000000];
string st;
vector<long long int> vec;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int TESTS, q, a, s, b, r, k, c, p, w, d, x, i, j, y, z, xs, ys, t;
  TESTS = 1;
  cin >> TESTS;
  while (TESTS--) {
    cin >> n;
    for (long long int i = 1; i <= 2 * n; i++) brr[i] = 0;
    for (long long int i = 0; i <= n - 1; i++) {
      cin >> arr[i];
      brr[arr[i]] = 1;
    }
    bool pos = true;
    for (long long int i = 0; i <= n - 1; i++) {
      an[2 * i] = arr[i];
      bool cur = false;
      for (long long int j = arr[i]; j <= 2 * n; j++)
        if (brr[j] == 0) {
          cur = true;
          an[2 * i + 1] = j;
          brr[j] = 1;
          break;
        }
      if (!cur) {
        pos = false;
        break;
      }
    }
    if (!pos) {
      cout << -1 << "\n";
      continue;
    }
    for (long long int i = 0; i <= 2 * n - 1; i++) cout << an[i] << " ";
    cout << "\n";
  }
  return 0;
}
