B: that because Nancy was required to write the
essay, it could not
possibly reflect her real opinions
Incorrect.
Research on the fundamental attribution error has shown
that even when people have good reason to believe that the causes for a
behavior are situational, they still overestimate dispositional factors.
So the professor's belief that Nancy could not believe what she wrote,
because she was assigned to do so, would contradict research on the fundamental
attribution error. The professor would probably believe that Nancy
actually believed what she wrote.