#include <bits/stdc++.h>
using namespace std;
const int MAX = 5e5 + 10;
int b[105], a[205], n;
int main() {
  int t;
  cin >> t;
  while (t--) {
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> b[i];
    map<int, int> mp;
    set<int> s;
    for (int i = 1, j = 1; i <= 2 * n; i += 2, j++) {
      a[i] = b[j];
      mp[a[i]] = 1;
    }
    for (int i = 1; i <= 2 * n; i++) {
      if (!mp[i]) s.insert(i);
    }
    bool flag = 1;
    for (int i = 2; i <= 2 * n; i += 2) {
      if (s.upper_bound(a[i - 1]) == s.end()) {
        flag = 0;
        break;
      }
      auto it = *s.upper_bound(a[i - 1]);
      a[i] = it;
      s.erase(it);
    }
    if (!flag)
      cout << -1 << endl;
    else {
      for (int i = 1; i <= 2 * n; i++) cout << a[i] << " ";
      cout << endl;
    }
  }
}
