In a four stroke cycle petrol engine, the expansion

A)
may start and end anywhere
B)
starts at top dead centre and ends at bottom dead centre
C)
starts at 30° after top dead centre and ends at 50° after bottom dead centre
D)
starts at 30° before top dead centre and ends at 50° before bottom dead centre

Correct Answer : Option (D) :   starts at 30° before top dead centre and ends at 50° before bottom dead centre