According to the invisible hand principle, competitive markets generally

a. bring the self-interest of individuals into harmony with the efficient allocation of resources, even though centralized planning of economic activities is absent.
b. bring the self-interest of individuals into harmony with the efficient allocation of resources when the behavior of individuals is directed by democratic centralized planning.
c. require central direction; otherwise, the actions of self-interested individuals will conflict with the general interests of society.
d. promote the economic welfare of self-interested producers at the expense of unorganized groups such as consumers and taxpayers.

A