Answer:
The efficient level of pollution removal occurs where the marginal benefit of pollution removal equals the marginal cost of pollution removal (some cow farts could be allowed).
Explanation:
This is the statement that would best fit within economic theory. If we look at this problem, we would see that there is a cost (the cost of removing pollution) and there is a benefit (the benefit of pollution removal). If we do not take the welfare of the Earth into account, then the best (most efficient) strategy to take would be one in which the marginal benefit of pollution removal equals the marginal cost of pollution removal. This would mean that it is not efficient to get rid of all cow farts. Instead, it is better to allow some in order to keep the cost of pollution removal low enough.