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