The electronics in the ignition coil and the powertrain control module in a compression-sensing ignition system can detect which of the two companion (paired) cylinders require higher voltage, which indicates the cylinder that's

a. on the power stroke.

b. at zero degrees bdc (bottom dead center).

c. on the compression stroke.

d. at zero degrees tdc (top dead center).

The answer is c) on the compression stroke.  

Explanation:

The compression stroke is the stroke in an engine in which the air or air/fuel mixture is compressed before ignition. The intake valve closes and the piston starts up on the compression stroke. During the compression stroke, the piston moves up the cylinder, squeezing the fuel-air mix.

the branch of biology that deals with the normal functions of living organisms and their parts.

the way in which a living organism or bodily part functions.