How Do Dieterle and Koolage Answer the Question, "What Are

How do Dieterle and Koolage answer the question, "What are the odds that 'a good guy with a gun could stop a mass shooter?"

A) All scientific studies confirm this claim
B) We have many scientific studies that confirm this claim
C) We do not have any scientific studies that confirm or disconfirm this claim
D) We have many scientific studies that disconfirm this claim
E) All scientific studies disconfirm this claim