单项选择题
A.hoisting system only
B.hoisting system and luffing system
C.hoisting system and slew and slewing system
D.slewing system only
单项选择题 Crude oil washing of cargo tanks has the following advantages except for （）
单项选择题 Where is the cooling water from the compensating tank in the cooling water system of main engine lead to?（）
单项选择题 From viewpoint of practice, it is sometimes important to detect abnormal happenings in the running gear by（）