#include <bits/stdc++.h>
using namespace std;
int n, a[209], vis[209], b[109];
set<int> s;
int main() {
  cin.tie(0);
  cout.tie(0);
  ios::sync_with_stdio(0);
  ios_base::sync_with_stdio(0);
  int t;
  cin >> t;
  while (t--) {
    cin >> n;
    s.clear();
    for (int i = 0; i < n * 2; i++) s.insert(i + 1);
    for (int i = 0; i < n; i++) {
      cin >> b[i];
      s.erase(b[i]);
    }
    for (int i = 0; i < n * 2; i += 2) a[i] = b[i / 2];
    bool no = 0;
    memset(vis, 0, sizeof(vis));
    for (auto it = s.begin(); it != s.end(); it++) {
      int b = -1, x = *it;
      for (int i = 0; i < n * 2; i += 2) {
        if (a[i] < x && b == -1 && vis[i] == 0) b = i;
      }
      a[b + 1] = x;
      if (b == -1) no = 1;
      if (no) break;
      vis[b] = 1;
    }
    if (no)
      cout << -1;
    else
      for (int i = 0; i < 2 * n; i++) cout << a[i] << " ";
    cout << "\n";
  }
}
