Hey there,
Your question states: Which of the following statements is Craig most actually testing?
Based on my information and understanding, I believe that your correct answer would be
.The reason why I said that this would be the correct answer would be because the other option include unnecessary ideas of Craig do experiments on that particular subject. The other options seem like they do not include the reason why it would really be important to do this thing. Your correct answer would be D.
Hope this helps.
~Jurgen