GMAT question - symantic problem?

[Sephus]

[ QUOTE ]
Knowing the textbook was wrong I chose the actual correct answer, and when it was marked as wrong when I got the test back I asked the professor why, pointing out that the textbook was wrong. His reply was, 'I know, but I was testing you on the book."

[/ QUOTE ]

the play here is to punch him in the face.