Although Cap and Trade Systems Reduce Total Emission for a Given

Although cap and trade systems reduce total emission for a given pollutant, they have been criticized because

A) the government does not specify how emission reduction will occur.
B) some companies make money by emitting less and selling their allowance.
C) local air quality can actually worsen when a factory purchases additional allowances.
D) once an total emission cap is set it remains at that level indefinitely