What characteristic of school bus seats contributes significantly to passenger safety?

Answer: B — They are closely spaced together

The characteristic of closely spaced school bus seats significantly contributes to passenger safety primarily because this design helps in minimizing movement within the bus during travel. By having seats positioned closer together, it reduces the potential for passengers to be thrown from their seats in the event of sudden stops, turns, or impacts. This layout supports better containment of passengers, particularly in the event of an accident, as it allows the seats to act as a protective barrier against injury. The other options, while they may offer certain conveniences or features, do not have the same direct impact on safety. Removable seats are beneficial for maintenance but do not enhance safety during transit. Adjustable height features, while accommodating for varying passenger needs, do not address the fundamental safety concerns associated with the overall design and spacing of seats. Lastly, leather upholstery may improve comfort and ease of cleaning, but again, does not play a crucial role in the safety mechanisms provided by the bus's design. Therefore, the design feature of closely spaced seating stands out as the most relevant to enhancing the safety of passengers on a school bus.