单项选择题
Officers use sextants to observe （）.
A. stars B. celestial bodies C. the sun D. the moon
单项选择题 The telegraph is the（）(设备)that connects the engine room and the bridge.
单项选择题 The captain wants to see the （）.
单项选择题 Echo sounder sends a（） (无线电信号)from the bottom of the ship to the seabed.
