When a Competitive Firm Has Reached a Level of Output

When a competitive firm has reached a level of output at which the marginal revenue product of each input is equal to the price of that input it:

A) is producing that output at least possible cost, but is not necessarily at maximum-profit output level.
B) is at its maximum-profit output level, but is not necessarily producing that output at least possible cost.
C) is at maximum-profit output level and is producing that output at least possible cost.
D) is not necessarily either at maximum-profit level of output or at least possible cost for that output.
E) is none of the above.