Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now, listen to the passage. According to the passage, the work of "Youth Summit" refers to
A．visits to the Nixon Library. B．the Chinese students’ visit to the U.S. C．a meeting discussing relations between China and the U.S. D．activities to strengthen the ties between the Chinese and American students.