Which of the following is prohibited regarding bus operation?

The focus on prohibiting certain behaviors while operating a bus is primarily centered around safety and the integrity of bus operations. Among the options, one specific prohibition relates to the operational integrity of the driver and how their physical condition can impact safety.

Operating a bus with excessively long nails can hinder a driver's ability to effectively control the vehicle, manipulate the controls, and respond swiftly in emergency situations. This creates a potential safety hazard, as any distraction or physical impairment while operating a bus can significantly jeopardize the safety of passengers, other vehicles, and pedestrians.

In contrast, other choices involve more direct safety violations, such as driving with distractions, transporting too many passengers, or age-related restrictions on passengers. While these actions are certainly problematic and could lead to penalties, the particular nature of excessive long nails poses a unique risk that affects the driver's operational ability in a more immediate sense. Therefore, this specific prohibition underscores the importance of ensuring that drivers maintain a level of physical readiness that is conducive to safe bus operation.