单项选择题
Containers are loaded and discharged by （）(龙门吊).
A. ship’s derricks B. fork trucks C. gantry cranes D. shore cranes
单项选择题 Our heavy derrick has been （）(不用)for a long time.
单项选择题 （）(调高) the derrick, please.
单项选择题 （）(降下)the derrick, please.
