单项选择题
The signal man assisting a crane operator has his arm extended with his fingers closed and thumb pointing upward. This is the signal to（）.
A.raise the boom B.raise the hook C.raise the boom and hook D.check the boom stop
单项选择题 The rope which is the lightest is（）.
单项选择题 The rope which is rove from the truck to be used with a bos’n chair is called a（）.
单项选择题 The rolling hitch could be used to（）.
