The fuel valve in a four stroke cycle diesel engine

A)
may open and close anywhere
B)
opens at top dead centre and closes at bottom dead centre
C)
opens at 15° before top dead centre and closes at 20° after top dead centre
D)
opens at 15° after top dead centre and closes at 20° before bottom dead centre

Correct Answer : Option (C) :   opens at 15° before top dead centre and closes at 20° after top dead centre