In a group of 68 students, each student is registered for at least one of three classes – History, Math, and English. Twenty-five students are registered for History, twenty-five students are registered for Math, and thirty-four students are registered for English. If only three students are registered for all three classes, how many students are registered for exactly two classes?
A. 13
B. 10
C. 9
D. 8
E. 7
Answer: B
Source: Manhattan GMAT