单项选择题
Questions 4 to 7 are based on the following conversation. At the end of’the conversation, you will be given 20 seconds to answer the questions. Now, listen to the conversation.
Which of the following details is CORRECT（）
A． Mark knows the exact number of airport buses.
B．Mark knows the exact number of delegates’ spouse.
C． Mark doesn’t know the exact number of delegates yet.
D． Mark doesn’t know the number of guest speakers.