Closed-ended questions are those questions which can be answered either with "yes" or "no”, or in other words, If you can answer a given question with a "yes" or "no" then such question is a closed-ended type of question. In contrast, open-ended questions are those which, instead of a one-word answer, require answers in the form of a list, a few sentences, paragraph or even an essay.
Keeping in mind the stated before, the example provided "why do cats’ eyes close in the dark?" is already an open-ended question since its answer could come in the form of a sentence or as a list of the reasons which would explain why cats’ eyes close in the dark. On the other hand, a Closed-ended question using the same example provided could be Do cats’ eyes close in the dark? whose answer would be either “yes” or “no”.
