There are 10 slate rocks, 15 pumice rocks, and 6 granite rocks randomly distributed in a certain field. If 2 rocks are chosen at random and without replacement, what is the probability that both rocks will be slate rocks?
Choose the most appropriate option:
A) 2 / 19 B) 3 / 31 C) 4 / 37 D) 5 / 41 E) 6 / 53

Rationale: "10 / 31 * 9 / 30 = 3 / 31 the answer is b ."
Answer: B