Final answer:
To check the functioning of the lubrication system, you should check the oil pressure gauge.
Step-by-step explanation:
The correct answer is C. oil pressure gauge. The oil pressure gauge is used to check the functioning of the lubrication system in a vehicle. The lubrication system ensures that the engine's moving parts are properly lubricated to reduce friction and prevent damage.
If the oil pressure gauge indicates low or no pressure, it may indicate a problem with the lubrication system, such as insufficient oil flow or a faulty oil pump. For example, if the oil pressure gauge reads zero, it could mean that the engine is not receiving enough oil, which can lead to engine damage if not addressed. On the other hand, if the oil pressure gauge indicates high pressure, it may suggest a clogged oil filter or a malfunctioning relief valve.