How should you signal the crane operator to raise the boom and lower the load?（）.
A. Extend arm with the palm down and and hold this position rigidly
B. Place both fists in front of the body with the thumbs pointing outward each other
Clasp hands in front of you body
D. Extend arm with the thumb pointing up, and flex the finger s in and out for as long as the load movement is desired
微信支付 
支付宝支付