Which One of the Following Students Is Displaying Intrinsic Motivation

Which one of the following students is displaying intrinsic motivation?

A) Annette loves to play the viola and so practices for at least an hour each day.
B) Bob works hard in his classes because his parents have promised to buy him a car if he gets at least a 3.5 grade-point-average this year.
C) Cassie does her math homework faithfully every night because she likes her teacher and wants to please him.
D) Dennis takes physics because he wants to become an engineer and make a lot of money.