比较and和or 
1) 并列结构中，or通常用于否定句，and用于肯定句。
2) 但有时and 也可用于否定句。请注意其不同特点：
There is no air or water in the moon.
There is no air and no water on the moon.
在否定中并列结构用or 连接，但含有两个否定词的句子实际被看作是肯定结构，因此要用and.
典型例题
---I don‘t like chicken ___ fish.
---I don‘t like chicken， ___ I like fish very much.
A. and; and B. and; but C. or; but D. or;and
答案C.否定句中表并列用or， but 表转折。
判断改错：
(错) We will die without air and water.
(错) We can‘t live without air or water.
(对) We will die without air or water.
(对) We can‘t live without air and water.
