At a route stop, a driver counted five students waiting but only four boarded. What should happen before the bus leaves?

1. The driver should determine where the missing student is and, if the student cannot be accounted for outside, secure the bus and check around and underneath
2. The driver should leave because most students boarded
3. The driver should ask traffic behind the bus to check the danger zone
4. The driver should back up to look for the missing student