What Happens to the Long-Run Equilibrium in the Competitive Market

What happens to the long-run equilibrium in the competitive market

A) In long-run equilibrium, marginal firms make a positive economic profit.
B) To maximize profit, firms should produce at a level of output where price equals marginal revenue.
C) The amount of gold in the world is limited; therefore, the gold jewellery market probably has a long-run supply curve that is upward sloping.
D) Long-run supply curves are typically less elastic than short-run supply curves.