Examples of grammatically correct sentences include which of the following?

A) The plaintiff should of told the defendant.
B) You're hearing will be on December 15th.
C) The plaintiff's allegations are vague.
D) The plaintiff should of told the defendant, and The plaintiff's allegations are vague.

Option C is grammatically correct because it properly uses the possessive form "plaintiff's" to indicate that the allegations belong to the plaintiff, and the sentence is structured correctly. Options A and B contain grammatical errors ("should of" instead of "should have" in A, and the misuse of "you're" instead of "your" in B), and option D is incorrect because it includes option A, which contains a grammatical error.