#include <bits/stdc++.h>
using namespace std;
set<int> prime;
void SieveOfEratosthenes(int n) {
  bool prme[n + 1];
  memset(prme, true, sizeof(prme));
  for (int p = 2; p * p <= n; p++) {
    if (prme[p] == true) {
      for (int i = p * p; i <= n; i += p) prme[i] = false;
    }
  }
  for (int p = 2; p <= n; p++)
    if (prme[p]) prime.insert(p);
}
void solve() {
  int n;
  cin >> n;
  vector<int> in(n), v;
  set<int> s, temp;
  for (int i = 0; i < n; i++) {
    cin >> in[i];
    s.insert(in[i]);
  }
  for (auto i : in) {
    v.push_back(i);
    int x = i + 1;
    while (s.count(x) || temp.count(x)) {
      x++;
    }
    v.push_back(x);
    temp.insert(x);
  }
  auto it = temp.end();
  it--;
  if ((*it) != (2 * n)) {
    cout << -1;
  } else {
    for (auto i : v) cout << i << ' ';
  }
  cout << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) solve();
}
