单项选择题
The（）(千斤索) is a wire used to take the weight off.
A. light derrick B. union purchase C. topping lift D. heavy derrick
单项选择题 The （）(双杆联吊) is that two booms are used with a single hook.
单项选择题 The （）(包装货) is loaded and unloaded by cargo sling.
单项选择题 The（）(折叠式舱盖) can fold slowly.
