How should you signal the crane operator to lower the boom?______.
A.With arm extended and fingers closed, point thumb downward
B.With arm extended downwards and forefinger pointing down, move hand in small horizontal circles
C.Extend arm with the palm down, and hold this position rigidly
D.With hands clasped in front of your body
正确答案：A
你应怎样指挥起货机手落放吊杆?伸开臂膀握紧拳头拇指向下
