#include <bits/stdc++.h>
using namespace std;
const long int full = 205;
int n;
int b[full], a[full];
bool f[full];
int find(int s) {
  int x = 0;
  for (int i = s + 1; i <= 2 * n; i++)
    if (f[i] == false) {
      f[i] = true;
      x = i;
      break;
    }
  return x;
}
void process() {
  for (int i = 1; i <= 2 * n; i++) f[i] = false;
  for (int i = 1; i <= n; i++) {
    a[2 * i - 1] = b[i];
    f[b[i]] = true;
  }
  int x;
  for (int i = 1; i <= n; i++) {
    x = find(b[i]);
    if (x == 0) {
      cout << "-1" << endl;
      return;
    }
    a[i * 2] = x;
  }
  for (int i = 1; i <= 2 * n; i++) cout << a[i] << " ";
  cout << endl;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  long int t;
  cin >> t;
  while (t--) {
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> b[i];
    process();
  }
  return 0;
}
