单项选择题 When two power-driven vessels are meeting head-on and there is a risk of collision,each shall（）.

单项选择题 The overall set in Malacca straight is to the NW, but from May to September there is a tendency for SE sets to prevail in some N and central parts.In this sentence,“set”refers to（）.

单项选择题 （）indicates the weight of the vessel and is,therefore,according to a well known principle of physics,equal to the weight of the water it displaces.