I came across the sentence below in a dictionary. Are the punctuation marks correctly used?

Could you please keep quiet, so that you won't waken the baby.

Seems O.K. to me Ryan.
Perhaps the comma is not neccessary, but I don't think it does any harm.
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Dear Mike,

A question mark is not used to end the sentence. This is because it is intended to be a request that expects no replies (rhetorical question). Am I right?

That's a curly one Ryan. You may be right, but I'm not sure.
'curly one' means?
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I think he means that it's a nasty question. I agree.

However, a question is a question. What's meant to be rhetorical is a matter of interpretation.

I vote for using a question mark.

If the 'Could you' was omitted at the start then the sentence is turned into a command so the question mark is not needed. With the 'Could you' included I believe that it is a question so should include a question mark.