#include <bits/stdc++.h>
using namespace std;
void solve(int n, int b[]) {
  set<int> s;
  int a[2 * n];
  for (int i = 0; i < (int)2 * n; i++) {
    s.insert(i + 1);
  }
  for (int i = 0; i < (int)n; i++) {
    s.erase(b[i]);
  }
  if (*min_element(s.begin(), s.end()) == 1 ||
      *max_element(b, b + n) == 2 * n) {
    cout << "-1\n";
    return;
  } else {
    for (int i = 0; i < (int)2 * n; i++) {
      if (i % 2 == 0)
        a[i] = b[i / 2];
      else {
        if ((s.upper_bound(b[i / 2])) != s.end()) {
          a[i] = *s.upper_bound(b[i / 2]);
          s.erase(*s.upper_bound(b[i / 2]));
        } else {
          cout << "-1\n";
          return;
        }
      }
    }
  }
  for (auto x : a) cout << x << " ";
  cout << "\n";
}
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int tc;
  cin >> tc;
  while (tc--) {
    int n;
    cin >> n;
    int b[n];
    for (int i = 0; i < (int)n; i++) {
      cin >> b[i];
    }
    solve(n, b);
  }
  return 0;
}
