Subject: mathqa
Question: x , y , and z are all unique numbers . if x is chosen randomly from the set { 6 , 7 , 8 , 9 , 10 , 11 } and y and z are chosen randomly from the set { 20 , 21 , 22 , 23 } , what is the probability that x and y are prime and z is not ?
Option: 
A: 1 / 12
B: 2 / 15
C: 3 / 20
D: 1 / 5
Answer: A