Answer:
Not all Medicare drug plans
Step-by-step 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".