When using a guide or helper to assist you in backing up a small commercial bus, what is the most important safety rule to establish?

1. The helper should stand directly behind the vehicle in the middle of the path
2. The driver must keep visual contact with the helper at all times; if visual contact is lost, the driver must stop the vehicle immediately
3. The helper should use a loud megaphone to shout steering commands
4. The driver should ignore the helper's hand signals and rely only on the rear camera