Which of the Following Sounds Most Like Recreation,as Your Textbook

Which of the following sounds most like recreation,as your textbook defines it?

A) a student's time between getting out of class and going to work
B) a guitarist on tour who has to sell T-shirts and CDs at the merchandise table after each show
C) the "recess" period given to children in primary school, when they can spend unstructured time on the playground
D) someone learning the calculus required to compute the amount and type of fuel needed to power a model rocket he wants to launch in a park