In the following conversation, which group discussion technique does han most clearly show?

emily:
han, i got to respectfully disagree with you. history professors wrote both of those books. ramona:
and history professors are reliable sources? emily:
[nodding] well . . yeah!

han:
o. k., normally i would get that. most history professors would be extra careful about using accurate details to make sure their claims are credible. but i did some extra research.

a. evaluating an author's point of view
b. asking clarifying questions
c. determining new research goals
d. challenging prevailing ideas