The enrollment in a certain course is 10% first-year students, 30% sophomores, 40% juniors, and 20% seniors. Experience has shown that the likelihood of receiving an A in the course is 0.2 for first-year students, 0.4 for sophomores, 0.3 for juniors, and 0.1 for seniors. Find the probability that a student who receives an A is a sophomore.
a.0.15
b.0.20
c.0.30
d.0.40