介绍： 版权归原作所有，仅供此学习，若有侵权请告知删除。
[12:09.65]The last reading.
[12:12.32]Snow
[12:14.00]Snow is a form of frozen water.
[12:17.36]It contains many groups of tiny ice particles called snow crystals.
[12:24.02]These crystals grow from water particles in cold clouds.
[12:29.74]They usually grow aro...

介绍： 版权归原作所有，仅供此学习，若有侵权请告知删除。
[12:09.65]The last reading.
[12:12.32]Snow
[12:14.00]Snow is a form of frozen water.
[12:17.36]It contains many groups of tiny ice particles called snow crystals.
[12:24.02]These crystals grow from water particles in cold clouds.
[12:29.74]They usually grow around a piece of dust.
[12:33.35]All snow crystals have six sides, but they grow in different shapes.
[12:39.82]The shape depends mainly on the temperature and water levels in the air.
[12:45.17]Snow crystals grow in one of two designs - platelike and columnar.
[12:52.51]Platelike crystals are flat.
[12:55.06]They form when the air temperature is about fifteen degrees below zero Celsius.
[13:01.97]Columnar snow crystals look like sticks of ice.
[13:06.82]They form when the temperature is about five degrees below zero Celsius.
[13:12.48]The shape of a snow crystal may change from one form to another
[13:18.02]as the crystal passes through levels of air with different temperatures.
[13:23.25]When melting snow crystals or raindrops fall through very cold air,
[13:29.30]they freeze to form small particles of ice, called sleet.