中考英语知识点：and与or的比较
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. 3 )表示选择的并列结构 (1) or 意思为"否则"。 I must work hard, or I'll fail in the exam. (2) either…or 意思为"或者……或者……"。注意谓语动词采用就近原则。
Either you or I am right. 判断改错： (错) They sat down and talk about something. (错) They started to dance and sang. (错) I saw two men sitting behind and whisper there. (对) They sat down and talked about something. (对) They started to dance and sing. (对)I saw two men sitting behind and whispering there. 解析： 第一句： and 连接两个并列的谓语，所以 talk 应改为 talked。 第二句：and 连接两个并列的动词不定式，第二个不定式往往省略to，因此sang 应改为 sing。 第三句：and 连接感观动词saw 后面的用作的宾补的两个并列分词结构，因此whisper应改为whispering。 注意：and 还可以和祈使句或名词词组连用表示条件。（or也有此用法） Make up your mind, and you'll get the chance. = If you make up your mind, you'll get the chance. One more effort, and you'll succeed. = If you make one more effort, you'll succeed.
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