A．They have been working at the telescope for two days.
B．They can’t find the microscope.
C．They’ve been working in the laboratory for two hours.
D．They can’t fix the microphone.

A．A good salesman should develop personal relationship with the customer first.
B．Grasping certain selling techniques is a must for a salesman.
C．A good salesman should adjust himself to different cultures.
D．A good salesman should know how to make use of trade shows.