#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> a(2 * n + 1), b(n + 1), c(2 * n + 1, 0);
    set<int> d;
    for (int i = 1; i <= n; i++) {
      cin >> b[i];
      c[b[i]] = 1;
    }
    for (int i = 1; i <= 2 * n; i++)
      if (!c[i]) {
        d.insert(i);
      }
    bool ok = true;
    for (int i = 1; i <= n; i++) {
      auto it = lower_bound(d.begin(), d.end(), b[i] + 1);
      if (it == d.end()) {
        ok = false;
        break;
      } else {
        a[2 * i - 1] = b[i];
        a[2 * i] = *it;
        d.erase(it);
      }
    }
    if (ok) {
      for (int i = 1; i <= 2 * n; i++) {
        cout << a[i] << (i < 2 * n ? ' ' : '\n');
      }
    } else {
      cout << -1 << endl;
    }
  }
  return 0;
}
