Analysis of test questions: A. Plasticizer contains three elements: carbon, hydrogen and oxygen, and is not an oxide, so the option is incorrectly stated.

The mass ratio of carbon, hydrogen and oxygen in plasticizer B is (12× 24): (1× 38): (16× 4) ≠12:19: 2, so the option is expressed.

C, plasticizer is composed of plasticizer molecules, 1 plasticizer molecules are composed of 24 carbon atoms, 38 hydrogen atoms and 4 oxygen atoms, 1 plasticizer molecules are composed of 66 atoms, so the option statement is wrong.

D The mass fraction of carbon in plasticizer is about 100%≈73.8%, so the option is expressed correctly.

So choose D.

Comments: This question is not difficult. Test students' ability to analyze and solve problems by combining new information and flexibly using the meaning of chemical formula and related calculations.