单项选择题
A Doppler log in the bottom return mode indicates the（）.
A.velocity of the current B.bottom characteristics C.depth of the water D.speed over the ground
单项选择题 A deadhead is a(n)（）.
单项选择题 A barometer showing falling pressure indicates the approach of a（）.
单项选择题 （）the canal transit，the radar was operating.
