20 1 1 in April, 2008, when the health department on the island of Taiwan Province Province carried out routine sampling inspection on food, it was found that a "pure probiotic" powder contained plasticizer DEHP. A, carbon compounds for organic matter, DEHP (chemical formula for C24H38O4), in line with the concept of organic matter, is correct, so A is not optional; B. DEHP (chemical formula is C24H38O4) is composed of three elements: carbon, hydrogen and oxygen, which is correct, so B is not optional; C DEHP (chemical formula is C2H4 38O4) is composed of molecules, and a C2H4 38O4 has 24 carbon atoms, 38 hydrogen atoms and 4 oxygen atoms, which is wrong, so C is optional;

D, according to the mass fraction of an element in the substance = relative atomic mass of the element × relative molecular mass of atomic number × 100%, and the mass fraction of hydrogen in C24H38O4 =1× 3812× 24+1× 38+00. Mass fraction of oxygen =16× 412× 24+1× 38+16× 4 ×100% =16.4%, and mass fraction of carbon =/. So choose C.