Although anyone can do it, storm chasing is extremely dangerous. The power of a big storm 31         throw a cow into the air 32         destroy a whole house in seconds. Storm chasers are also often hurt in accidents 33          (cause) by driving in 34         heavy rain. If you are a 35         (begin), it is much safer to join a group for storm-chasing vacations 36____________ the storm season.

However, for storm chasers, it is all worth it . “37                   you get 38            (close)to a storm, it is the most 39             (excite) sight you will 40             see in your life,” says Jasper Morley. “Every storm is an example of the power of nature. It is the greatest show on Earth.”

根据杂质含量的不同，工业纯铜可分为（）。

A.2种

B.3种

C.4种

D.5种