Consider a family with a mother, father, and two children. Let A1 = {mother has influenza}, A2 = {father has influenza}, A3 = {first child has influenza}, A4 = {second child has influenza}, B = {at least one child has influenza}, C = {at least one parent has influenza}, and D = {at least one person in the family has influenza}.

Are A3 and A4 mutually exclusive? Give a reason for your answer

Express D in terms of B and C.