The correct answer is D.
What did you like about your summer vacation?
STEP-BY-STEP EXPLANATION:
Open-ended question: An open-ended question is a question that cannot be answered with a "yes" or "no" response, or with a static response. Open-ended questions are phrased as a statement which requires a response.
Open-ended questions allow respondents to include more information, including feelings, attitudes and understanding of the subject. This allows researchers to better access the respondents' true feelings on an issue.
