Fructose and Galactose Both Have Six Carbon Atoms, Twelve Hydrogen

Fructose and galactose both have six carbon atoms, twelve hydrogen atoms and six oxygen atoms, just like glucose. A friend of yours says: "Since those sugars have the same number of atoms, they should have the same name." You answer: "While they do have the same number and type of atoms,

A) they are named differently because one is found in RNA and the other in DNA."
B) they are named differently because they cannot be converted into glucose."
C) they are named differently because they have different secondary structure."
D) they are named differently because they are isomers of the monosaccharide, glucose."
E) they are all polysaccharides and have slightly different functions within organisms and therefore have different names."