When your vessel is proceeding to the area of traffic density，（）is used to determine the exact ranges of other ships or objects in the vicinity.

When navigating using DGPS（Differential Global Position...

单项选择题When navigating using DGPS（Differential Global Positioning System）you may expect your position to be accurate to within a radius of（）.

What does not contribute to the commercial GPS receiver...

单项选择题What does not contribute to the commercial GPS receiver position error（）.

To obtain accuracy in fixing by DF，（）and three stations...

单项选择题To obtain accuracy in fixing by DF，（）and three stations should be used.