How Do the Primary Structures of Normal Hemoglobin and Sickle

How do the primary structures of normal hemoglobin and sickle cell hemoglobin differ?

A) A glutamic acid residue in normal hemoglobin is replaced by a valine residue in sickle cell hemoglobin.
B) A valine acid residue in normal hemoglobin is replaced by a glutamic acid residue in sickle cell hemoglobin.
C) There are four heme groups in normal hemoglobin whereas there are only three heme groups in sickle cell hemoglobin.
D) There are three heme groups in normal hemoglobin whereas there are 4 heme groups in sickle cell hemoglobin.
E) Both A and C are correct.