There are 35 students in a class. Among them, 25 students read fiction books or nonfiction books, while the rest of them do not read books at all. There are 18 student who read fiction books, and 15 students who read nonfiction books. The number of students who only read nonfiction books is …
a. 3
b. 7
c. 10
d. 15
e. 33