用所给词的适当形式填空。

     I'm Carol. Do you know how I study English? Well, vocabulary is the 1.________ (important) thing for me to study.  I always listen to the English program on the radio. When I hear some new words, I try 2.        (keep) them in my mind. Then after one or 3. ______(twice) days, I still remember some of them. I don't learn English just from English lessons. I learn it in 4.______ (difference) ways. Of course, I read some 5.        (interest) stories in English. I also speak a lot. To speak to myself is a good way. Many people don't like to do that. But I like doing that.

氨制冷剂系统管道、附件、阀门及填料的材质不应采用( )。

A．钢质材料
B．铸铁材料
C．铜或铜合金材料
D．无规定