""When we were discussing thermodynamics the other day, Dave didn't say anything. That must mean he doesn't know anything about the topic." What would be the most useful question to debunk this claim?"

Answer

the most useful question to debunk this claim is

Could there be another reason why Dave remained quiet?

Explanation:

Because its possible Dave could have known something but he choose to be quite because of another reason, as thus will debunk that he knows nothing about the topic

the answer is a. hope this .