Which of the Following Is an Example of a Self-Serving

Which of the following is an example of a self-serving bias?

A) Leonard attributes earning a good grade in his psychology class to the fact that he is an exceptionally hard working student who is also incredibly smart. He blames the poor grade he received in his sociology class on having a bad teacher who gave hard exams.
B) Leonard gets a bad grade in his psychology class and a good grade in his sociology class, so he believes he should study harder to prepare for his next psychology exam.
C) Leonard gets bad grades in sociology and psychology, so he switches his major to biology because he will like it more.
D) Leonard gets good grades in sociology and psychology, so he sends his professors a card thanking them for what good professors they are.