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 know 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.