What is moral hazard?

a. it refers to the actions people take before they enter into a transaction so as to mislead the other party to the transaction.
b. it refers to the actions people take after they have entered into a transaction that makes the other party to the transaction worse off.
c. it refers to the private, self-interested actions that people pursue, which when taken collectively leads to a loss in economic surplus.
d. it refers to the situation in which one party to a transaction takes advantage of knowing more than the other party to the transaction.