Detailed Instructions: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
Q: Possible Duplicate: What is the correct possessive for nouns ending in s? Before you vote to close as a duplicate, note that these two questions deal with similar issues to this, but none of them address all three criteria of this question: The singular already ends with an s. I am dealing with multiple of the thing. I want the possessive of all of them in general. The singular is class, and the plural is classes. The singular possessive is class's (as addressed here). What is the plural possessive? Is it classes's, or classes'?.
A:
It is classes', which sounds the same as the singular class's. I would have thought this was a general rule for plural nouns ending -s', -es' or -ies'.