The sentence that contains an adverbial clause is:
"Whether students have enough time to rest depends on how much homework they’re assigned."
The clause "Whether students have enough time to rest" acts as a noun clause serving as the subject of the sentence, but if you're looking specifically for an adverbial clause, "how much homework they’re assigned" serves that purpose, providing information about the dependence. Since none of the sentences contain a typical adverbial clause (which usually starts with subordinating conjunctions like 'because,' 'although,' 'when,' etc.), it might be more accurate to choose the second sentence given its structure regarding dependency.
However, if defining strictly, none of the options provided have traditional adverbial clauses, the focus should instead be on the context of dependency in the second structure.