Which of the Following Is Not True in a Long-Run $P = M C$

Multiple Choice

Which of the following is not true in a long-run perfectly competitive equilibrium?

A) $P = M C$ , where P is market price and MC is the marginal cost of a firm.
B) $P = A C$ , where P is market price and AC is the average cost of a firm.
C) $Q ^ { d } = n q$ , where $q$ is the supply of an individual firm,
$n$
is the number of firms in the industry, and Q^d is the market demand for a product.
D) Firms may earn negative profits.