Question

In which sentence does an adverb clause modify an adverb?

Answer 1

The correct answer to the question stated above is:

The scientists studied the sun as the eclipse’s shadow swept across Earth. 

Adverb clause consists of words which function as an adverb. It can modify verbs, adverbs, and adjectives by providing conditions to describe them. 

Answer 2

The snetence in which an adverb clause modifies an adverb is "The scientists studied the sun as the eclipse’s shadow swept across Earth." Option A is correct.

Adverb clause consists of words which function as an adverb. It can modify  or describe verbs, adverbs, and adjectives by providing conditions.

Adverb clauses can be employed to add explanatory detail to your writing and explain how or why things happen.