In Which of the Following Situations May Tradeable Pollution Permits

Multiple Choice

In which of the following situations may tradeable pollution permits be preferred to Pigovian taxes?
(i) where they internalise the externality of pollution
(ii) where regulatory agencies do not know the demand curve for pollution
(iii) where the government is not interested in generating maximum revenue from polluting firms

A) (i) only
B) (ii) only
C) (ii) and (iii) only
D) (i) , (ii) and (iii)