This is an example of an external benefit. When the employees of a corporation become stockholders, then the problem of shirking ends. The owner's property right to the residual income of the firm provides owners with a strong incentive to keep per unit costs of production low. Both a and b are correct. The rate of return that owners of capital must receive in order to induce them to continue supplying the capital is often referred to as accounting profit.
Firms can better exploit team production than market coordination of production.
Firms avoid some of the transaction costs associated with market coordination of production. All of the above correctly answer the question.