Answer:
d. relies on incentives to reduce the pollution externality.
Step-by-step explanation:
Negative Externality is negative side effect on third party , without any compensation for the same. Pollution is a negative externality , as it has extra social cost (negative impact) on society.
Coase Theorum is internalising of externality cost , by bargaining between two parties. Moral codes to reduce pollution externality include creating social awareness & consciousness. Foreign Discrimination is completely unrelated. So, all these points are completely inapt.
Singapore's case of imposing fine on littering : signifies incentive approach to reduce pollution externality. Such because : not littering creates a self monetary incentive for the person - of saving the fine amount, which he / she could have lost if he / she could have littered.