How should you signal the crane operator to move slowly?（）.
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
