"What closed?" or "What did close?"
If someone said:
"The park closed"
and another one heard that something closed but he don't know what it is, what should he use to ask:
"What closed?" or
"What did close?"
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I read that we don't need to add a helping verb ("did" in this case) if we ask about the subject, then the correct sentence -according to this rule- would be "What closed?".
Am I right ?