单项选择题
Which one of the following rules is not regarding two power-driven vessels meeting end or nearly end on so as to involve risk of collision（）.
A.Each shall keep her course and speed B.Each shall alter her course to starboard C.Each shall pass on the portside to the other D.Each shall indicate such action by one short blast on the whistle
单项选择题 Which display indicates a vessel conducting mineclearance operations（）.
单项选择题 When you doubt the existence of risk of collision,（）.
单项选择题 When visibility is restricted（），we can say it is restricted visibility.
