Subject: mathqa
Question: x , y , and z are all unique numbers . if x is chosen randomly from the set { 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: 3 / 20
B: 1 / 5
C: 1 / 8
D: 3 / 10
Answer: C