#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> b(n);
    vector<int> q;
    unordered_set<int> s;
    for (int i = 0; i < n; i++) {
      cin >> b[i];
      s.insert(b[i]);
    }
    for (int i = 1; i <= 2 * n; i++) {
      if (s.count(i) == 0) q.push_back(i);
    }
    vector<int> perm;
    bool p = true;
    for (int i = 0; i < 2 * n && p; i++) {
      if (i % 2 == 0) {
        perm.push_back(b[i / 2]);
      } else {
        auto it = lower_bound(q.begin(), q.end(), b[i / 2]);
        if (it == q.end()) {
          cout << -1 << endl;
          p = false;
        } else {
          perm.push_back(*it);
          q.erase(it);
        }
      }
    }
    if (p) {
      for (int i : perm) {
        cout << i << " ";
      }
      cout << endl;
    }
  }
}
