Using the Punnett squares, determine the possible blood types of the offspring and the ratio of phenotypes when:
a) Father is type O, and mother is type AB.
b) Father is type A, heterozygous, and mother is type B heterozygous.
c) Father is type B, homozygous, and mother is type A, homozygous.
d) Father is type AB, and mother is type AB.