Question

what is the purpose of the underlined part of the sentence? during the summer bears eat enormous amounts of food in preparation for their winter hibernation. it is an adverbial clause that explains how bears eat. it is a noun phrase that acts as the object of the verb eat. it is a prepositional phrase that provides more information about hibernation. it is an independent clause that provides more information about bears.

Explanation:

An adverbial clause modifies a verb, adjective, or another adverb, often answering questions like when, where, why, how. In "During the summer bears eat enormous amounts of food in preparation for their winter hibernation", "in preparation for their winter hibernation" explains why bears eat a lot, which is an adverbial - like function. A noun phrase would act as a subject, object, etc. and this isn't the case here. It's not a prepositional phrase acting as the object of "eat" as the object of "eat" is "enormous amounts of food". It's not an independent clause as it can't stand alone as a complete sentence.

Answer:

It is an adverbial clause that explains how bears eat.