#include <bits/stdc++.h>
using namespace std;
const int maxn = 210;
bool vis[maxn];
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<long long> v;
    memset(vis, 0, sizeof(vis));
    for (int i = 0; i < n; i++) {
      long long x;
      cin >> x;
      v.push_back(x);
      vis[x] = 1;
    }
    bool flag = 1;
    vector<long long> res;
    for (int i = 0; i < n; i++) {
      bool f = 0;
      res.push_back(v[i]);
      for (int j = v[i] + 1; j <= 2 * n; j++) {
        if (!vis[j]) {
          res.push_back(j);
          vis[j] = 1;
          f = 1;
          break;
        }
      }
      if (!f) {
        flag = 0;
        cout << -1 << endl;
        break;
      }
    }
    if (flag) {
      for (int i = 0; i < res.size(); i++) cout << res[i] << ' ';
      cout << endl;
    }
  }
}
