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.

Ryan
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?

Ryan
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.
Agreed.

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.