Directions: In this section, you’ll hear some passages. At the end of each passage, you'll hear some questions. Both the passage and the questions will be spoken only once. After each question, choose the best answer from the four choices marked A, B, C, and D. Questions 15 to 17 are based on the passages you have just heard.[音频]
A. 1,000.
B. 2,500.
C. 5,500.
D. 8,000.