Suppose that a flower nursery benefits from having a butterfly farm located only a few miles away, because the presence of the insects greatly improves flower pollination. Lawyers for the two companies meet to draft a legal document specifying the number of butterflies the farm promises to maintain in exchange for payments to be made by the nursery. Which of the following types of private solutions to the externality of pollination has occurred in this case?
A) Integration of different types of businesses through merger or acquisition
B) Charities
C) Moral codes and social sanctions
D) Contracts