#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
int a[205], b[105];
set<int> st;
int n;
void solve() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> b[i];
  st.clear();
  for (int i = 1; i <= 2 * n; i++) st.insert(i);
  for (int i = 1; i <= n; i++) {
    st.erase(b[i]);
  }
  if (st.size() != n) {
    cout << -1 << endl;
    return;
  }
  for (int i = 1; i <= n; i++) {
    a[2 * i - 1] = b[i];
  }
  for (int i = 2; i <= 2 * n; i += 2) {
    auto tmp = st.upper_bound(a[i - 1]);
    if (tmp == st.end()) {
      cout << -1 << endl;
      return;
    }
    a[i] = *tmp;
    st.erase(tmp);
  }
  for (int i = 1; i <= 2 * n; i++) {
    cout << a[i] << " ";
  }
  cout << endl;
}
int main() {
  ios::sync_with_stdio(false);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
