单项选择题
A.in use
B.prior to use
C.after use
D.When chart received on board
单项选择题 What is the distance from the bottom of a wave trough to the top of a wave crest?（）
单项选择题 Depths in the routes (Malacca and Singapore Straits) vary between 20m and about 23m but there are many areas of sand waves and depths are liable to change. The statement infers that（）.
单项选择题 The lifeboat is constructed of（）