I think the bolded words would be "whom Mr. Stein chose". The clause whom Mr. Stein chose is an example of an adjective because the clause describes the word student. Student is the subject of the sentence and is a noun. An adjective describes a noun or another subject. an adverb describes a verb or another adverb.
Mature or adult would be your answer.
Answer:
The main idea is most people don't know we are in the middle of a bionic revolution.
Supporting detail 1: 220,000 people walk around with cochlear implants
Supporting detail 2: Tens of thousands of people have been implanted with deep brain stimulators
