In determining safe speed，all of the following must be taken into account EXCEPT the（）.

单项选择题When a vessel sees the other ahead or nearly ahead，by night she could see the masthead lights of the other in a line or nearly in a line or both side lights，（）shall be deemed to exist.

A.head-on situation
B.end-situation
C.crossing situation
D.close-quaters situation

单项选择题When in sight of another vessel，any action taken to avoid collision must（）.

A.be accompanied by sound signals
B.not result in another close quarters situation
C.include a speed change
D.All of the above

单项选择题When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision，they shall be deemed to be in（）.

A.crossing situation
B.head-on situation
C.restricted visibility
D.overtaking situation

单项选择题When you doubt the existence of risk of collision,（）.

A.such risk shall be deemed to exist
B.such risk shall not be deemed to exist
C.you needn't take any action to avoid collision with any vessel
D.you should accelerate your speed ahead

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