An open-ended question encourages a long answer that relates to the answerer's feelings. A closed-ended question will result in one-word, short answers.
The answer is A. What did you like about your summer vacation? This question can give a wide range of answers that would give the asker info about the answerer's feelings towards the vacation. The other three questions are all closed-ended, as they can be answered with one word or short statements, and they do not provide any further detail into the answerer's feelings.
