Normally, how many seats that are not securely fastened to the bus are allowed?

In a passenger bus, safety regulations dictate that all passenger seats must be firmly secured to the vehicle to ensure the safety of passengers during travel. The primary concern is that unsecured seats can pose significant hazards in the event of sudden stops or accidents, potentially causing them to shift and injure individuals. Therefore, the regulation stipulating that no seats should be unsecured aligns with the overarching goal of maintaining a safe environment for all passengers. Ensuring that the total number of unsecured seats remains at zero maximizes passenger safety, which is why this answer is correct.

Other options suggest allowing a certain number of unsecured seats, which undermines this safety principle. In transit operations, prioritizing the protection of passengers is essential for compliance with safety standards and regulations.