听力原文： Can you imagine ice that does not melt and is not wet.'？ Have you ever heard of

dry ice？ Dry ice is made by freezing a gas. It is quite different from ordinary ice, which is simply frozen water.

Dry ice was first manufactured in 1925. It has fulfilled the hopes of its inventor. It can be used for making artificial fog in the movies. When steam is passed over dry ice, a very dense vapor rises. It can also be used for destroying insects in grain supplies. It is more practical than ordinary ice be cause it takes up less space and is 142 degrees colder. Since it turns into steam instead of melting in to water, it is cleaner to use. For these reasons it is extremely popular, and many people prefer it to ordinary ice.

What is dry ice made of？

A．Chemicals.

B．Vapour.

C．Water.

D．Gas.