Question

Which best completes the sentence? Those muffins in the oven certainly smell __________ .

a. good
b. well A?

Answer 1

They certainly smell good. "good" is referring to the smell-a good, smell   So it's an adjective.

Answer 2

a) good

a muffin is a noun and good is an adjective and adjectives modify nouns.
well is an adverb and adverbs modify verbs