How many cylinders should be used for driving on level roads with light loads on the M915?

Answer: B — 2

The M915 is designed to optimize fuel efficiency and performance under various load and terrain conditions. When driving on level roads with light loads, it is most efficient to engage two cylinders. Using two cylinders allows the engine to operate efficiently without wasting fuel while still providing enough power for light loads. Engaging more cylinders than necessary could lead to reduced fuel economy, as the engine would be consuming more fuel than required for the lighter conditions. This balance of power and efficiency is crucial for modern heavy trucks like the M915, which are often equipped with advanced engine management systems allowing for such selective cylinder operation. This practice is part of managing the vehicle's performance effectively in different driving environments.