单项选择题
A.velocit in knot
B.irection from which it flows
C.estimated current
D.direction toward which it flows
单项选择题 Several shoals（）reported to exist in the area south-west of the Brothers.
单项选择题 A system of cleaning the tanks by washing them with the cargo of crude oil while it is being discharged is known as（）.
单项选择题 A vessel emitting harmful substances into the air or spilling oil into the sea is a（）.