The red blood cells of people with sickle cell anemia have abnormal shapes due to ____.

A) hemoglobin molecules with mutant beta globin subunits sticking together and forming long fibers in the cytoplasm
B) destruction of the hemoglobin molecules
C) loss of hemoglobin through leaky cell membranes
D) the attachment of phosphate groups to the hemoglobin molecules
E) the binding of methyl groups to the heme group of the hemoglobin molecule causing desiccation of the cells