单项选择题
A.Radio communications allow the crane operator to disregard the use of hand signals
B.The crane operators and signalman must be familiar with the correct hand signals
C.The forward cranes can be operated from the bridge
D.The aft cranes can be operated from the aft steering station
单项选择题 Which of the following statements is TRUE regarding automatic identification systems（AIS）（）.
单项选择题 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.
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（）.