The Demand for Labor of a Perfectly Competitive Producer

The demand for labor of a perfectly competitive producer:

A) is perfectly elastic at the going wage rate.
B) is downward sloping because prices fall when the producer increases output.
C) is downward sloping because of diminishing marginal productivity.
D) is downward sloping because prices fall when the producer increases output and because of diminishing marginal productivity.
E) is downward sloping because of diminishing marginal utility.