Assuming a Downward-Sloping Demand Curve,a Decrease in Production Costs for Firms

Multiple Choice

Assuming a downward-sloping demand curve,a decrease in production costs for firms in a perfectly competitive market initially in long-run equilibrium will cause a(n) :

A) permanent increase in the price.
B) economic profit for firms in the short run.
C) increase in demand.
D) increase in firms' marginal revenue.