Final answer:
Engine idling affects fuel efficiency and a company's bottom line due to unnecessary fuel consumption, but does not impact vehicle acceleration. Therefore, the correct answer to the question would be 'both A and B'.
Step-by-step explanation:
When discussing engine idling, it is important to understand the impacts it has both on fuel efficiency and on a company's bottom line. Idling results in unnecessary fuel consumption which certainly reduces fuel efficiency as the engine uses fuel without contributing to vehicle motion. For businesses that rely on a fleet of vehicles, fuel costs can be significant, so extra fuel spent during idling directly affects the company's expenses.
However, engine idling has no direct impact on how quickly a vehicle can accelerate once the engine is engaged in powering the vehicle forward. Therefore, the correct answer to the question would be 'both A and B'.