单项选择题
The average height of the surface of the sea for all stages of the tide over a 19 year period is called（）.
A.mean high water B.mean low water C.half-tide level D.mean sea level
单项选择题 The 3-cm radar as compared to a 10-cm radar with similar specifications will（）.
单项选择题 The “urgent” priority should be used for messages（）.
单项选择题 The “horse latitudes” are regions of（）.
