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（）.

单项选择题Which display indicates a vessel conducting mineclearance operations（）.

A.Three balls in a vertical line
B.Two balls in a vertical line
C.One ball near the foremast and one ball at each yardarm
D.One diamond near the foremast and one ball at each yardarm

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 visibility is restricted（），we can say it is restricted visibility.

A.by long distance
B.by the darkness at night
C.by a vessel in front
D.by fog or falling snow

单项选择题When underway in a channel，you should keep to the（）.

A.Middle of the channel
B.Starboard side of the channel
C.Port side of the channel
D.Side of the channel that has the widest turns

单项选择题When underway in a channel，you should if safe and practicable（）.

A.stay near the middle of the channel
B.keep to the starboard side of any vessels you meet
C.exchange whistle signals with any other vessels in the channel
D.keep to the side of the channel which lies to your starboard