单项选择题
A.an oil content meter
B.an oil checker
C.an analyzer of oil content
D.a mixer of oily water
单项选择题 Air gap is the vertical distance between the bottom of the hull and the（）.
单项选择题 According to regulations，access to a cargo pumproom in a tanker carrying grades C or D liquid cargo shall be（）.
单项选择题 Access to a cargo pumproom on a tanker carrying grades A，B，C or D liquid cargoes shall be（）.