Which One of the Following Is the Best Example of a Student

Which one of the following is the best example of a student working for an incentive?

A) Arnold's teacher gives him a big hug after he surprises her by bringing her a cupcake from home.
B) Betsy decides not to talk in class because her teacher ridiculed her earlier in the day when she gave an incorrect answer.
C) Cyril stays out late even though he knows he will be punished when he gets home.
D) Doris is studying with the hope that she'll get a high grade on her history test.