单选题 In the passage, the author is primarily concerned with

• (A) presenting a hypothesis and describing compelling evidence in support of it
• (B) raising a question and describing an important discovery that led to an answer
• (C) showing that a certain autoimmune disease cannot yet be treated effectively with drugs
• (D) explaining what evidence exists for an autoimmune cause for narcolepsy
• (E) discussing the importance of research on animals for the study of human disease