单项选择题
A.head-on situation
B.crossing situation
C.overtaking situation
D.close-quarters situation
单项选择题 Chart/Publication correction record Card system ensures that every chart is properly corrected（）.
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（）.