What hazardous materials may be carried on a school bus?

The correct answer focuses on the specific situation where oxygen, which is a hazardous material when not properly contained, is medically prescribed for a student. This exception is made because the transportation of prescribed medical oxygen is necessary for certain students' well-being and does not pose a general risk to others on the bus when managed appropriately.

In general, hazardous materials are carefully regulated due to the potential harm they can cause. Most types of hazardous materials, especially those not related to medical needs, cannot be carried on school buses to ensure the safety of all passengers.

The choice involving firearms carried by civilians or police officers would typically not be allowed on school buses, as such items present significant safety risks and are subject to strict laws and protocols. Thus, only medically necessary items like prescribed oxygen are considered permissible for transport on school buses, under proper guidelines and precautions.