Question

what is an engine combustion stroke?
a) when the piston moves down drawing air and fuel into the cylinder.
b) when the piston moves up causing the air/fuel mixture to combust.
c) when the spark plug ignites and the piston is forced to the bottom of the cylinder.
d) when the piston moves up forcing the exhaust to combust.

Explanation:

In an engine's combustion stroke, the spark - plug ignites the compressed air - fuel mixture, and the resulting explosion forces the piston downwards. Option A describes the intake stroke, option B is the compression stroke, and option D is incorrect as exhaust doesn't combust in the way described.

Answer:

C. When the spark plug ignites and the piston is forced to the bottom of the cylinder.