#include <bits/stdc++.h>
using namespace std;
double getTime() { return clock() / (double)CLOCKS_PER_SEC; }
void read(){};
template <typename T, typename... Args>
void read(T& a, Args&... args) {
  cin >> a;
  read(args...);
}
void print(){};
template <typename T, typename... Args>
void print(T a, Args... args) {
  cout << a << " \n"[sizeof...(args) == 0];
  print(args...);
}
void solve() {
  int n;
  cin >> n;
  vector<int> a(n);
  vector<int> cnt(201, 0);
  for (int i = 0; i < n; i++) {
    read(a[i]);
    cnt[a[i]] = 1;
  }
  vector<int> ans;
  for (int i = 0; i < n; i++) {
    ans.push_back(a[i]);
    int k = 1;
    while (cnt[a[i] + k]) k++;
    ans.push_back(a[i] + k);
    cnt[a[i] + k] = 1;
    if (a[i] + k > n + n) {
      print(-1);
      return;
    }
  }
  for (auto x : ans) cout << x << ' ';
  puts("");
}
int main() {
  int t;
  read(t);
  while (t--) solve();
}
