How do commas work within sentences?

Use a comma between two long independent clauses when conjunctions such as and, or, but, for, nor connect them. Example: I have painted the entire house, but she is still working on sanding the floors. Rule: If the clauses are both short, you may omit the comma.

write a five paragraph essay, you were taught to have three body paragraphs. a university essay is more flexible than that, depending on its length and on what it is trying to say. a short university essay may have three body paragraphs, but it may have more.

its specific purpose is to sell a product to people .

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