In Order to Study Labor Markets More Easily, We Make

In order to study labor markets more easily, we make which of the following assumptions about firms? (i)
Firms sell their products in competitive markets.
(ii)
Firms buy their inputs in competitive markets.
(iii)
Firms maximize profits.
(iv)
Firms maximize revenues.

A) (iii) only
B) (i) and (iii) only
C) (i) , (ii) , and (iii) only
D) (i) , (ii) , (iii) , and (iv)