#include <bits/stdc++.h>
long double pi = 3.14159265358979;
using namespace std;
int inf = 1e9;
void fastIO() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
}
void solve() {
  int n;
  cin >> n;
  vector<int> a(2 * n);
  vector<bool> cur(2 * n, true);
  for (int i = 0; i < 2 * n; i += 2) {
    cin >> a[i];
    a[i]--;
    cur[a[i]] = false;
  }
  for (int i = 1; i < 2 * n; i += 2) {
    int pos = inf;
    for (int j = 2 * n - 1; j >= 0; j--)
      if (cur[j] && j > a[i - 1]) pos = min(pos, j);
    if (pos == inf) {
      cout << -1 << "\n";
      return;
    }
    a[i] = pos;
    cur[pos] = false;
  }
  for (int i = 0; i < 2 * n; i++) cout << a[i] + 1 << " ";
  cout << "\n";
  return;
}
int main() {
  fastIO();
  int t;
  cin >> t;
  for (int i = 0; i < t; i++) solve();
  return 0;
}
