Subject: mathqa
Question: there are 15 slate rocks , 20 pumice rocks , and 10 granite rocks randomly distributed in a certain field . if 2 rocks are to be chosen at random and without replacement , what is the probability that both rocks will be slate rocks ?
Option: 
A: 7 / 22
B: 7 / 66
C: 2 / 45
D: 1 / 3
Answer: B