Mr. Smith has bought a new house in the country, around ____ some green trees.     [ ]

A. which is      

B. it is      

C. which are      

D. them are

二氧化碳灭火系统设置在粉尘或喷漆作业等场所的喷头，应增设不影响喷射效果的（）。

A、保护罩

B、防护罩

C、防尘罩

D、安全罩