There are two kinds of grammar based on different linguistic points of view. They are prescriptive grammar and descriptive grammar. A grammar may describe how language is actually spoken and/or written, and may not state or postulate how it ought to be spoken or written. But a grammar may also state the rules for what is considered the best or most correct usage. Which grammar is descriptive grammar, and which grammar is prescriptive grammar？ Cite some examples to give your reasons.（北师大2003研)

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