单项选择题
[听力原文] W: Do you want me to explain these problems before your mid-term exam M: That’s a good idea. I have trouble learning the material.
A．Boss and secretary. B．Doctor and nurse. C．Teacher and student. D．Lawyer and client.
A．Usually SBS can be easily paid little attention to. B．SBS can occur in all the new buildings. C．SBS mostly happens in a poorly ventilated, airtight building. D．SBS is said to be caused by one of two general categories of pollution.
A．With the help of PSAs, the ground crews and scientists can present in real time in the spacecraft. B．With the help of PSAs, the ground crews and scientists can control the spacecraft as if they were there. C．With the help of PSAs, the ground crews and scientists cannot in real time present in the spacecraft. D．With the help of PSAs, the ground crews and scientists cannot advise the astronauts to deal with different situations.