#include <bits/stdc++.h>
using namespace std;
void compute() {
  int n;
  cin >> n;
  vector<int> ft(n);
  vector<int> res(2 * n);
  for (int i = 0; i < n; ++i) {
    cin >> ft[i];
    ft[i]--;
  }
  set<int> st;
  for (int i = 0; i < 2 * n; ++i) {
    st.insert(i);
  }
  for (int i = 0; i < n; ++i) {
    st.erase(st.find(ft[i]));
  }
  for (int i = 0; i < n; ++i) {
    res[2 * i] = ft[i];
    set<int>::iterator it = st.upper_bound(ft[i]);
    if (it == st.end()) {
      printf("%d\n", -1);
      return;
    }
    res[2 * i + 1] = *it;
    st.erase(it);
  }
  for (int i = 0; i < 2 * n; ++i) {
    printf("%d ", res[i] + 1);
  }
  printf("\n");
}
int main() {
  int t;
  cin >> t;
  for (int tc = 0; tc < t; ++tc) {
    compute();
  }
  return 0;
}
