When Sam’s science teacher assigns the class some online reading assignments about marine biology, Sam races home after school. He is excited to start reading—he wants to learn as much as he can about the subject because he is planning a career in marine biology. He studies the reading material closely, memorizing the difficult words and taking many notes. When it comes time for the test, he gets a high grade, improving his overall class grade as a result. What is the main reason Sam is so actively engaged with the text he is reading?

He wants to do well on the upcoming test.
He needs to increase his understanding of difficult vocabulary.
He wants to improve his overall class grade.
He is highly interested in the subject matter.