Which of the Following Calculations Described in the Following Statements

Which of the following calculations described in the following statements require that you use the addition rule?

A) Calculate the probability of black offspring from the cross AaBb × AaBb,when B is the symbol for the black allele.
B) Calculate the probability of children with both cystic fibrosis and polydactyly when parents are each heterozygous for both genes.
C) Calculate the probability of each of four children having cystic fibrosis if the parents are both heterozygous.
D) Calculate the probability of a child having only sickle-cell anemia or cystic fibrosis if each parent is each heterozygous for both traits.