#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const int maxn = 100 + 10;
int n;
int b[maxn];
int ans[2 * maxn];
void solve() {
  cin >> n;
  map<int, int> m;
  m.clear();
  for (int i = 1; i <= n; i++) {
    cin >> b[i];
    m[b[i]] = 1;
    ans[2 * i - 1] = b[i];
  }
  for (int i = 1; i <= n; i++) {
    for (int j = b[i] + 1;; j++) {
      if (j > 2 * n) {
        puts("-1");
        return;
      }
      if (m[j] == 0) {
        m[j] = 1;
        ans[2 * i] = j;
        break;
      }
    }
  }
  cout << ans[1];
  for (int i = 2; i <= 2 * n; i++) cout << ' ' << ans[i];
  cout << endl;
}
int main() {
  long long T;
  scanf("%lld\n", &T);
  while (T--) solve();
  return 0;
}
