A small pond contains four catfish and two bluegill. If four fish are caught at random, what is the probability that all of them are catfish?

a) 1/15 ≈ 6.667%

b) 1/4080 ≈ 0.025%

c) 1/720 ≈ 0.139%

d) 1/20 ≈ 5%