第一节 听下面5段对话。每段对话后有一个小题，从题中所给的A、B、C三个选项中选出最佳选项，并标在试卷的相应位置。听完每段对话后，你都有10秒钟的时间来回答有关小题和阅读下一小题。每段对话仅读一遍。 Why did the woman thank the man

A. It is difficult to find out how the brain works.
B. After an arm is cut off, the doctors cannot put it back.
C. We should stop studying the brain because it is so dangerous.

A．experience
B．things
C．books
D．school