The answer is A, true.
There is a quizlet (search the same question in go0-gle) that mentions this question, I’d suggest to give it a look if you have any problems answering questions.
The correct answer is 'phenomenon'. A phenomenon is any event that is observable, however common it may be.
"exuberance" means enthusiasm or showing a lot of energy. if someone holds back a cry of pain, that doesn't really make them seem energetic or excited. from that alone, you can infer that "stoicism" is your answer, but that word relates to a pointed lack of emotion, like when someone doesn't want to lose face or show that they're in pain.
A noun phrase is formed by a noun or pronoun, this one receives the name of the head, and any dependent words before or after the head. Dependent words are the ones that give specific details about the head. An example of a noun phrase can be: <em>a quantifier + a determiner + an adjective + a noun.</em> However, there are some others that are longer and with more dependent words.
Following this concept the two noun phrases in the text are:
<em>1. Senior citizens and others who need medical assistance </em>
<em>2. The subset of the US population with Medicare</em>
