Red Blood Cells That Phenotyped as [Le(a-B-)] Are Incubated with Plasma

Red blood cells that phenotyped as [Le(a-b-) ] are incubated with plasma containing Le^a substance. The red blood cells convert to the phenotype [Le(a+b-) ]. Whereas the same red blood cells incubated with saliva containing Le^a substance do not convert. Why?

A) Glycoproteins are not absorbed onto red blood cell membranes.
B) Biochemically, Lewis substances in saliva are glycolipids.
C) Only Le^b substance in saliva can convert phenotypes.
D) Other enzymes found in the saliva interfere with the conversion from Le(a-b-) to Le (a+b-) .