How should you signal the crane operator to use the main hoist?（）.

A.Use one hand to give any miotion signal , and place the other hand motionless in front of the hand giving the motion signal

B.Extend arm with the thumb pointing up , and flex the fingers in and out for as long as the load movement is desired

C.First tap your elbow with one hand , and then proceed to use regular signals

D.First tap the top of your head with your first , and then proceed to use regular signals

停车调查的内容包括（）和（）两个方面。