There are 10 slate rocks, 11 pumice rocks, and 4 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 one:
A) 3 / 20
B) 5 / 26
C) 7 / 34
D) 9 / 37
E) 11 / 49

Rationale: "10 / 25 * 9 / 24 = 3 / 20 the answer is a ."
Answer: A