Answered

Which phrases in this information about Medicare prescription drug coverage are noun phrases? Medicare offers prescription drug coverage to help senior citizens and others who need medical assistance get the prescription drugs they need, under Part D of the program (or Part C if you are enrolled in the Medicare Advantage Plan). The subset of the US poplutation with Medicare can join a drug plan to get this coverage. Not all Medicare drug plans are the same, however. Look for the “Medicare Approved” seal on drug discount cards to make sure you are getting the best deal.

Answer :

I am very sure it is part C. My cousin had same homework and he put part B but I think that is wrong.
annyksl

Answer:

Not all Medicare drug plans

Explanation:

A sentence is classified as a noun phrase when it does not have a verb in its composition, so it is formed mainly by names: nouns, adjectives and adverbs.  However, some authors dispute the existence of noun phrases, stating that the verb is merely understood, being mentalized in the interlocutors of communication.

Therefore, since the noun phrase is one that does not have an explicit verb, the noun phrase present in the text shown in the question is  "Not all Medicare drug plans".