What Does It Mean If a Question Is Considered "Closed

What does it mean if a question is considered "closed?"

A) Only one group of students has been selected to respond to the question.
B) The time has run out for the group to respond to the question.
C) A response will be accepted only after additional explanation.
D) The question is more of a statement; no response is needed.
E) The question has only one expected and correct response.