单项选择题
A.within two hours
B.within three hours
C.within four hours
D.within five hours
单项选择题 It is dangerous for vessels without the operational radar（）the estuary.
单项选择题 Bales close to the deckhead should be covered to prevent（）.
单项选择题 The force resulting from the earth’s rotation that causes winds to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere is called（）.