Sorry if I'm wrong
The answer is: D. Valve timing
Valve timing refers to the exact timing when the piston engine is being either opened or closed. The closing and opening of the piston engine regulates the cylinder filling process. Which means that by setting the valve timing correctly, we can optimize the amount of airflow that got into the machine and keeps the engine from overheating.
I've taken test
A. valve lift
B. push rod
C. intake manifold
D. valve timing. I think the answer is letter A.
mr sandman bring me an g make it the oogiest that ive ever seen