Each Breed of Dog Is Known to Be Susceptible to Certain

Each breed of dog is known to be susceptible to certain illnesses, such as heart problems, eye disorders, or thyroid problems. Often, dog breeders will go to great lengths to breed a dog that's unrelated to a dog they want to breed. This is because

A) individuals closely related are more likely to have the same deleterious genes.
B) individuals closely related are less likely to want to mate.
C) breeding individuals that are closely related may produce an interesting new set of characteristics.
D) breeding individuals that are closely related will result in greater fitness for the offspring.