A．They probably grow up in poor families.
B．They are born to experience failures.
C．They probably have been spoiled by indulgent parents.
D．They may have received undue frustrations in childhood.

A．An efficient allocation of resources is realized through perfect competition.
B．Perfect competition can be realized where monopolies are absent.
C．The "invisible hand" checks and balances the economy.
D．Adam Smith advocates the promotion of self-interest.