单项选择题
The ARQ mode should be applied（）.
A.when two stations communicate with each other B.in any radio system and at any time C.when one ship sends a message to another station D.for communication among some stations
单项选择题 Signals for locating will be transmitted in the 9GHz band by means of（）.
单项选择题 A ship station on receiving a shore-to-ship distress alert should（）.
单项选择题 What channel is general communication used?（）
