单项选择题
A barometer showing falling pressure indicates the approach of a（）.
A.high pressure system B.low pressure system C.high dew point D.low dew point
单项选择题 （）the canal transit，the radar was operating.
单项选择题 （）should be used during the poor visibility if the radar’s screen shows heavy sea returns.
单项选择题 （）is on the panel of radar.
