Question

spark plugs either use a ______ design or a washer type of gasket to form a seal between the spark plug and the cylinder head.

a. combustion
b. rough
c. smooth
d. taper

Explanation:

Spark plugs can use a taper design or a washer - type gasket. The taper design is a common method to create a seal. Combustion is related to the process in the engine, not the seal design. Rough and smooth are more about surface finish in general terms and not specific seal - forming designs for spark plugs.

Answer:

d. Taper