Final answer:
Valve overlap is the period during an engine's cycle when both intake and exhaust valves are open at the same time, which helps in expelling exhaust gases and allowing a fresh charge to enter. The correct answer to the question is A) Overlap.
Step-by-step explanation:
The term valve overlap refers to the time period within an engine's cycle when both the intake and exhaust valves are open simultaneously. This occurs towards the end of the exhaust stroke and the beginning of the intake stroke. The purpose of valve overlap is to improve engine efficiency by helping to expel all the exhaust gases and drawing in a fresh charge of the air-fuel mixture or air in the case of direct injection engines.
The correct answer to the question 'Valve blank is the time when both of the valves in a cylinder are open' is A) Overlap. Neither clearance, duration, nor timing are terms that describe the simultaneous opening of intake and exhaust valves in an engine cylinder.