湖南省郴州市2015暑假
高考英语阅读理解练习（4）及答案阅读理解----1 today, ultrasonic(超声的) waves are being put to work in laboratories and factories. if an ultrasound generator is placed in a liquid, the waves move the liquid back and forth hundreds of thousands of times each second. this causes materials to mix quickly or to dissolve(使分解，使溶解) in liquids. paint manufactur
