问题：

[单选] How should you signal the crane operator to swing?（）.

A . With both arms extended out and palms to down, move arms back and forth
B . With arm ertended downwards and forefinger pointing down,move hand in small horizontal crecles
C . Extend arm and point finger in the direction to move boom
D . Place both fists in front of the body with the thumbs pointing outward