"In order to judge whether there is a risk of collision with an

"In order to judge whether there is a risk of collision with an approaching vessel, the mariner can ____.

A.judge the movement of the approaching vessel only by sight

B.use ARPA whcih can plot that automatically or plot the vector triangle with seim-automatic plotting device

C.keep her course and speed

D.both A and B"

正确答案是B