单项选择题
What is meant by the term two-blocked（）.
A.The bottom block touches the top block B.The line has jumped the sheaves C.There are turns in the fall D.You have two blocks
单项选择题 The use of（）between bags may lead to chafe and tearing of the bags.
单项选择题 The tackle that raises and lowers the boom is（）.
单项选择题 The strongest of the natural fiber ropes is（）.
