Sickle-cell anemia is a genetic disease caused by the presence of a faulty hemoglobin gene (HbS). The normal version of this gene is HbA. Which of the following is TRUE about HbS and HbA?

a) It is impossible for a person to carry two HbS genes.

b) They’re both alleles for the same trait.

c) A person with two HbS genes would be a silent carrier.

d) Hemoglobin genes are always inherited from one’s mother.

e) People carrying two HbS genes smell like rotten fish.