Although Plant Biomass Is Plentiful for Use as Biofuel,which Major

Although plant biomass is plentiful for use as biofuel,which major problem needs to be overcome?

A) Increasing the efficiency of breakdown of cellulose into glucose.
B) Decreasing the cost of production of plant biomass.
C) Increasing the production of cars that can run on ethanol.
D) Polluting by-products of the conversion of glucose to ethanol.
E) Increasing use of biofuels may drive crop prices down.