Read the sentence. Although Molly loved her grandfather’s visits, she sometimes became frustrated when he insisted she engage in an afternoon-long discourse about life. In this sentence, the word discourse functions as _[blank]_. Which answer best completes the sentence?
A.an adjective that means “related to discussion”
B.an adverb that means “in a talkative way”
C.a noun that means “lengthy discussion”
D.a noun that means “serious argument”