【单选题】

Questions 17 to 20 are based on the following passage.At the end of the passage, you will be given 20 seconds to answer the questions. Now, listen to the passage.

How does the speaker say a direct quotation should be usedA．It should be assimilated thoroughly.
B．It should be enclosed in quotation marks.
C．It should be paraphrased by the author.
D．It should be authorized by the sourc