Final answer:
The requirement for buses and vehicles used for hire or lease to carry a chemical type fire extinguisher was instituted in the mid-1970s.
Step-by-step explanation:
In the United States, the requirement for buses and vehicles used for hire or lease to carry a chemical type fire extinguisher was instituted in the mid-1970s. Therefore, the correct answer to this question is b. 1975. This requirement ensures the safety of passengers and helps to prevent and control fires in these vehicles. It's crucial for vehicles that carry passengers to have the correct safety equipment, and a fire extinguisher is typically mandatory. These regulations ensure that, in the event of a fire, there is a means of potentially controlling or extinguishing the fire to promote the safety of passengers and the operator.