Question

Which sentence uses the correct comparative form of closely?

A.
The stallion follows closer than the donkey.

B.
Joe rides closelier than Fred.

C.
Ana follows more closely than Marisol.

I think A.

Answer 1

I would say that the choice for the correct comparative form would be:Ana follows more closely than Marisol. I believe this is correct because by using "more closely" is makes the comparison very clear about who follows the closest.

Answer 2

The correct answer is C. Ana follows more closely than Marisol.
The word closely is an adverb, which means that its comparative form is created by adding the word more in front of it, and the word most if you want to create the superlative form.
If this were an adjective close, then the comparative form would indeed be closer. But given that it is an adverb, their comparative forms differ.