单项选择题
In Section A, B and C you will hear everything once only. Listen carefully and then answer the questions that follow.
SECTION A TALK
Questions 1 to 5 refer to the talk in this section. At the end of the talk you will be given 15 seconds to answer each of the following five questions. Now listen to the talk.
A．to introduce categories of books in US libraries.
B．to demonstrate the importance of US libraries.
C．to explain the roles of different US libraries.
D．to define the circulation system of US libraries.