Which of the following components serves as both a cover for the bottom of the engine block and a reservoir for engine oil? a. front cover b. valve cover c. oil pan d. lubrication retainer

I believe the answer is C. oil pan
Oil pan usually bolted on the bottom of the crankcase (even though in most cases it's made to be detachable) to cover the bottom of engine block.
It is also molded on the bottom of the crankcase so it could be used as oil reservoir.

Pressure and heat that's what i think( don't report if wrong)

Answer/runoff from agricultural feedlots