What condition must the entry door of a school bus meet before use?

The entry door of a school bus must operate smoothly and close securely from the inside to ensure the safety of the passengers, especially children. This requirement is critical because it prevents any accidental opening of the door while the bus is in motion, which could lead to serious injuries. A door that operates smoothly ensures that bus drivers can easily manage passenger boarding and disembarking without complications, contributing to efficient and safe operation. Additionally, the ability for the door to close securely from the inside means that passengers are safeguarded inside the bus, further enhancing safety protocols designed for student transport.

The other options do not adequately meet the safety standards necessary for a school bus. For instance, if a door could only close from the outside, it would pose significant risks during emergency situations, where a quick, secure exit may be needed. Similarly, while remote locking might be a useful feature, it does not address the fundamental need for the door to operate effectively and securely from within, which is crucial during regular operations and emergencies.