单项选择题
The （）(双杆联吊) is that two booms are used with a single hook.
A. derrick B. union purchase C. topping lift block D. crane
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.
单项选择题 The（）(侧滚式舱盖) runs along the guide rail.
