按照标准划分，火灾共分为哪几类？
参考答案：特别重大火灾、重大火灾、较大火灾和一般火灾。
环境保护法主要解决的环境问题称为（）。
A.第一环境问题
B.第二环境问题
C.资源问题
D.人口问题
Pupils often want to sit next to their particular friend and many classroom activities involve moving about, but even relatively small alterations can make ______ to the visual comfort of pupils with sight defects.
A. a difference B. an interference C. a modification D. an impact
