If you need to back up a bus without a look out, you should `_________`.

A Set the parking brake, turn off the motor and take the keys with you and walk to the rear of the bus to determine whether the way is clear.

explanation

If you need to back up your vehicle but you do not have a look out, you should set the parking brake, turn off the motor and take the keys with you and walk to the rear of the bus to determine whether the way is clear.