While reading the newspaper Cindy saw a circular graph that showed the number of A's in the senior English class as 20%, the number of B's in class was 30%, the number of C's was 40% and the number of failures was 10%. In picking one student at random, what is the probability that the student earned a C in this class

A: 1/10

B:1/5

C:1/3

D:2/5