How should you signal the crane operator to lower

How should you signal the crane operator to lower the boom and raise the load ________．

A.Extend arm and point finger in the direction to move the boom

B.Extend arm with thumb pointing downward and flex fingers in and out

C.With forearm vertical and forefinger pointing up，move hand in small horizontal circles

D.With arm extended downwards and forefinger pointing down，move hand in small horizontal circles

请帮忙给出正确答案和分析，谢谢！