Irene knows her body type is A, but William does not know his blood type. However, William knows that his mother and father both had blood type B. Irene and William's first child is a boy with type O blood. Based on this info, William's blood type could be
a. B only
b. either B or O
c. O only
d. either AB or O
e. A only
Answer: b. either B or O