单项选择题
A.When a risk of collision exists
B.When action by the give-way vessel alone will not prevent a collision
C.When the bearing to give-way vessel becomes steady
D.When the vessels become less than 1/2 mile apart
单项选择题 When one upbound vessel is overtaking another vessel and both are pushing a tow ahead，what reaction may you expect（）.
单项选择题 When one of two vessels（）is required to keep out of the way the other must keep her course and speed.
单项选择题 When a vessel is in any doubt as to whether such a situation exists she shall（）that it does exist and act accordingly.