Which of the following should be checked in the engine compartment?

In the context of a CDL Class B Pre Trip Inspection, checking the engine compartment is crucial for ensuring the vehicle's safe operation. The correct choice focuses on key components that directly impact engine performance and reliability.

Assessing oil levels is essential because sufficient oil lubrication is necessary to prevent engine wear and overheating. Checking coolant levels is equally important as it helps maintain the engine at an optimal operating temperature, preventing it from overheating. Belts and hoses should also be examined to ensure they are in good condition, without any signs of cracks or wear, as they play vital roles in various engine functions, such as coolant circulation and power transmission.

These components collectively contribute to the engine's efficiency and can help prevent breakdowns or accidents caused by engine failure. The other options listed pertain to different parts of the vehicle or are not specifically related to the engine compartment, making them irrelevant in this specific context.