When you doubt the existence of risk of collision,（）.

单项选择题When your vessel enters thick fog，she should sound（）every two minutes in accordance with these Rules.

A.one short blast
B.one prolonged blast
C.two short blasts
D.three short blasts

单项选择题Where does the look-out man stand?（）.

A.In positions in which the noises in the ship are least likely to interfere with the hearing of a fog signal and the man can see clearly
B.In positions in which the noises in the ship are much likely to interfere with the hearing of a fog signal
C.In positions in which the hearing of a signal is reduced to a minimum
D.In a position in which the man can see clearly

单项选择题While underway at night you observe a vessel’s range lights in line off your starboard beam． You should（）.

A.come right
B.sound the danger signal
C.continue on your course
D.come left

单项选择题You are in restricted visibility and hear a fog signal forward of the beam. Nothing appears on your radar screen. You must（）.

A.stop your engines
B.sound two prolonged blasts of the whistle
C.sound the danger signal
D.slow to bare steerageway

单项选择题You are approaching another vessel and are not sure whether danger of collision exists. You must assume（）.

A.there is a risk of collision
B.you are the give-way vessel
C.the other vessel is the give-way vessel
D.there is no risk of collision