What Difference Between Sickle Cell and Normal Hemoglobin Is Apparently

What difference between sickle cell and normal hemoglobin is apparently responsible for all of the symptoms associated with sickle cell anemia?

A) The difference is a valine substitution in the mutant sickle cell hemoglobin for a glutamic acid in the normal molecule.
B) The difference is a glutamic acid substitution in the mutant sickle cell hemoglobin for a valine in the normal molecule.
C) The sickle cell hemoglobin is longer.
D) The sickle cell hemoglobin is shorter.
E) The sickle cell hemoglobin is translated backwards.