Final answer:
The phrase 'to browse for new books' is an infinitive phrase, beginning with 'to' followed by a verb and functioning as an adverb in the sentence.
Step-by-step explanation:
The phrase 'to browse for new books' in the sentence 'Before class, Ava always visits the library to browse for new books.' is an infinitive phrase. An infinitive phrase usually begins with the word 'to' followed by the base form of a verb and can include objects or modifiers. In this case, the phrase is functioning as an adverb, describing the purpose of visiting the library. However, the correct answer is A. infinitive phrase because that describes the form of the phrase, not its function within the sentence.