The magneto air gap is a precision measurement that's taken between the
a. edge of the flywheel and the ignition coil armature.
b. two breaker point contacts.
c. spark plug terminal and the ignition coil.
d. center electrode and the grounding electrode of a spark plug

option a) "edge of the flywheel and the ignition coil armature"

is correct.

Explanation:

A heat engine contains a type of electronic ignition system that consists of a magnetic flywheel and a coil . When the flywheel is in motion , it triggers the coil to produce charge that is sent to spark plug to create fire in the heat engine.

the independent variable, the one that is intentionally manipulated, is whether or not the car hits the barrier.

the dependent variable, the one that you measure the response in, is the distance that the washers travel.