#2016年职称英语《卫生类》概括大意练习（8） 搜索结果
1.Childrenenjoyshoutingatahighwallandhearingthesoundebacktothem.Thesesoundsarecalledechoes（回声）.Echoeshavegivenusanumberofvaluabletools.2.Echosoundingdeviceswereearlyusedinmakingmapsoftheoceanfloor.So
