超声换能器(探头)的作用是() A.发射超声波 B.接收超声波 C.发射和接收超声波 发布时间:2017-09-03 05:22 │ 来源:www.tikuol.com 题型:单项选择题 问题: 超声换能器(探头)的作用是()A.发射超声波B.接收超声波C.发射和接收超声波D.放大超声波E.滤过超声波
题型:单项选择题 He ________ your car by mistake because he didn't have the keys. A.mustn't have takenB.shouldn't have takenC.couldn't have takenD.needn't have taken 查看答案