The appropriate follow-up question to ask this student, according to the text you added in the comment box, would be the second one: "<em>What are the health problems caused by sugary drinks?</em>"
Explanation:
The other questions would also be accurate if the conversation continues, but, as a follow-up question to this student's comment, the second one would be the one because it is directly related to his statement and digs deeper into the subject he is talking about.
