Which of the following is an example of a theme?

A. A working college student misses out on fun activities, but is hard work helps him appreciate his degree.

B. Gene's hard work pays off in the end, and he graduates from the university at the top of his class.

C. Gene has to work nights to pay for college and is unable to attend all the cool parties.

D. Sacrifices and hard work pay off in the end, despite the challenges along the way.