#include <bits/stdc++.h>
#pragma GCC optimize("O2")
using namespace std;
signed main() {
  long long nn;
  cin >> nn;
  while (nn--) {
    long long n;
    cin >> n;
    vector<long long> vec(n + 1);
    vector<long long> res(2 * n + 1);
    vector<long long> vissited(2 * n + 1, 0);
    for (long long i = 1; i <= n; ++i) {
      cin >> vec[i];
      res[2 * i - 1] = vec[i];
      vissited[vec[i]] = 1;
    }
    bool ctr = 0;
    for (long long j = 1; j <= n; ++j) {
      long long cur = vec[j] + 1;
      while (cur <= 2 * n and vissited[cur] == 1) cur++;
      if (cur == 2 * n + 1) {
        cout << -1 << "\n";
        ctr = 1;
        break;
      }
      vissited[cur] = 1;
      res[2 * j] = cur;
    }
    if (ctr) continue;
    for (long long k = 1; k <= 2 * n; ++k) {
      cout << res[k] << " ";
    }
    cout << "\n";
  }
  return 0;
}
