第17题:[单选题] What often happens when using echo-sounder at river estuary where a layer of fresh water lies on the top of denser salt water? A.A scattering layer appears. B.Echo sounder stops working. C.shallow water appears. D.Nothing abnormal happens. 参考答案:A 【参考译文】在高密度海水之上有一层淡水的河口使用回声测深仪时将发生什么?出现散射层。 【解 析】scattering layer散射层