The optimizes airflow, keeps cylinder pressure in a certain range, and determines the engine's operating range.
a. valve lift
b. push rod
c. intake manifold
d. valve timing

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.

c. the net deposit amount.

accelerated heartbeat, raise in blood pressure, slow in digestion, raise in blood sugar and perspiration. (myers' psychology for ap 2nd edition pg 87)