21. (B)
Question Type: Analyze Argument Structure
This argument begins with the conclusion, then offers a supporting premise, then provides a more specific example of that premise. Answer (B) correctly identifies the second sentence’s role as a premise, or "an explanation of" the conclusion.
(A) is incorrect. The claim is a premise, not a conclusion.
(C) does identify the claim in question as being a premise, but misstates the claim it supports.
(D) refers to a claim that is nowhere to be found in the argument.
(E) inverts the relationship between the second and third sentences. The third sentence is an example of the second.