Answer:
B). The subset of the US population with Medicare
C). Not all Medicare drug plans.
Step-by-step explanation:
Noun phrases are elucidated as the group or cluster of words that together functions as a noun in the sentence. These words functions together as a unit and act as either the subject of verb or the object of the preposition or verb. It could easily be identified by checking the possibility of its substitution with a pronoun. In the given excerpt, the phrases 'the subset of the US population with Medicare' and 'not all Medicare drug plans' are the noun phrases as they function as nouns/subjects in the sentence and could easily be substituted with a pronoun. Thus, options B and C are the correct answers.