Ultrasonic waves can shake a liquid so fast that tiny holes form all through it. The liquid is actually torn apart by this action. Almost as soon as these holes are made, they fall together again. The result is a powerful pounding action. In the dairy industry this is used for the double purpose of making homogenized(使均匀，使匀质) milk and sterilizing(使无菌) it at the same time. If you look at some raw milk with a microscope, you find that it is made up of little drops of butter fat floating around in a watery liquid. In order to make milk easier to digest, these fat droplets(微粒) may be broken up by forcing the milk through very small openings. The result is called homogenized milk. When the ultrasonic method is used, the sound waves not only break up the droplets but also kill the germs in the milk by pounding them to pieces. (from www.nmet168.com)

　　1. Why does a paint manufacturer use ultrasound to do a better job of blending colors?

　　A. Because it is cheap to use ultrasound to blend colors.

　　B. Because the waves move the liquid so quickly that it can make materials mix quickly or dissolve in liquids.

　　C. Because they can mix chemicals by the use of sound waves.

　　D. Because the waves can clean the paint.

　　2. What properties does ultrasound wave have?

　　A. Homogenizes and sterilizes the milk.

　　B. Mix materials and break droplets.

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