You Can Either Read a Book, Get Something to Eat

You can either read a book, get something to eat, or take a nap. The opportunity cost of getting something to eat is _____

A) the cost of what you eat.
B) the difference between the costs of the book and the food.
C) the difference between the opportunity costs of reading and sleeping.
D) the net benefit of sleeping.
E) impossible to determine because the most preferred alternative is not known.