The figure shown below indicates two diseases with genetic links that are common in industrialized nations. The fact that both are about 80–90 percent avoidable indicates that
a. people are most likely avoiding having children with individuals who are affected by these diseases.
b. these diseases are most likely affected by environmental factors in addition to genes.
c. these diseases are Mendelian traits that are expressed more frequently in industrialized nations where the average life span is longer.
d. industrialized nations can use more resources to track these diseases in populations.