单项选择题
The boom stops on a pedestal crane prevent the boom from（）.
A.being raised too high B.swinging at sea C.overloading when not in use D.being lowered too low
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（）.
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（）.
