A、BECAusE thEir EnvironmEnt is BEComing morE AnD morE Dirty.
B、BECAusE thE trADitionAl wAys oF trEAting wAstEs ArE not EFFiCiEnt.
C．BECAusE thEy ArE short oF usEFul mAtEriAls.
D．BECAusE thEy nEED nEw mAtEriAls mADE From gArBAgE.