During the valve overlap period, the exhaust pressure of a turbocharged, four-stroke cycle diesel engine must be less than the intake manifold pressure to ensure __________.

Correct Answer: Option A — effective cylinder scavenging and cooling

During valve overlap in four-stroke engines, maintaining intake manifold pressure higher than exhaust backpressure ensures a positive scavenging sweep. Fresh, cool air cleans out residual exhaust gases and cools the combustion chamber components.