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.
These poems share a common concern about nature and how the seasons affect the growth of plants and crops.
Noun is They/Him
article is the sack
adjective is canvas