OG详解-OG2 文法 Q6

Choice C is the best answer. The convention being tested is punctuation between a main clause and a supplementary noun phrase. This choice correctly uses a comma to mark the boundary between the main clause (“scholar…materialism”) and the supplementary noun phrase (“an apt assessment”) that describes Waid’s observation about how The House of Mirth depicts the upper classes of New York society. 
Choice A is incorrect because a semicolon and the conjunction “and” can’t be used in this way to mark the boundary between a main clause and a supplementary noun phrase. Choice B is incorrect. Joining the main clause (“scholar…materialism”) and the following noun phrase with the conjunction “and” results in a confusing and illogical sentence that suggests that the novel depicts the upper classes of New York society as “an apt assessment,” which doesn’t make sense in this context. Choice D is incorrect because it fails to mark the boundary between the main clause and the supplementary noun phrase with appropriate punctuation.