单项选择题
On the approach of a warm front the barometric pressure usually（）.
A.falls B.rises C.is steady D.is unreliable
单项选择题 On a nautical chart，the inner ring of a compass rose indicates（）.
单项选择题 Navigational warnings are published according to（）.
单项选择题 Many navigational warnings are of a temporary nature，but others remain in force for several months or may be succeeded by（）.
