Answer:
OA: Support the crankshaft, control end play, provide a replaceable wear surface and dissipate heat.
Step-by-step explanation:
Main bearings are essential components of internal combustion engines. They serve the following functions:
Support the crankshaft: Main bearings support the weight of the crankshaft and allow it to rotate smoothly.
Control end play: Main bearings prevent the crankshaft from moving too far in either direction, which could cause damage to the engine.
Provide a replaceable wear surface: Main bearings are made of soft metal that wears over time. This protects the crankshaft from wear and tear.
Dissipate heat: Main bearings help to dissipate heat away from the crankshaft.
All of the above functions are essential for the proper operation of an internal combustion engine. Therefore, the best answer is OA.
OB, C, and D are incorrect because they do not describe all of the functions of main bearings.