One common grammar rule that even native speakers forget is in showing possession. This is a common theme in the English language. When showing possession with "your", be careful not to be confused with "you're" or "you are". For example, in this sentence, "The library book is not yours, so you're reminded to take good care of it." One way of remembering this rule is to replace the contraction with the phrase "you are" to check if it fits correctly.
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