单项选择题
（）the canal transit，the radar was operating.
A.At B.In C.During D.With
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.
单项选择题 （）20 targets can be tracked at one time．When maximum tracking capacity is reached，no further acquisitions are possible.
