What are the two classes of pure substances?

a. atoms and molecules
b. solutions and mixtures
c. elements and compounds
d. liquids and gases

Which statement is the best summary of the model? a-a series of aerobic and anaerobic reactions take place in cells b- the sun's energy moves through trophic levels in a food chain c-light energy is converted into stored chemical energy plants.d- food molecules are broken down in the cells if living things.