The first, second, and third workers employed by a firm add 24, 18, and 9 units to total product respectively. Therefore, we can conclude that:

A.  marginal product of the third worker is 9.
B.  the third worker has to work with poorer-quality tools and raw materials.
C.  the firm will not want to hire more than three workers.
D.  the first worker puts forth more effort than the second and third workers.