Why Would a Profit-Seeking Firm Need to Tailor Its Decisions

Why would a profit-seeking firm need to tailor its decisions about the quantity of labor inputs that it purchases?

A) to produce the highest profitable quantity of output at the lowest possible marginal cost
B) deciding what quantity to produce is one of the major choices a profit-seeking firm makes
C) the quantity of labor is the only variable cost choice a profit-seeking firm can make
D) to produce the profit-maximizing quantity of output at the lowest possible average cost