If Firms Enter a Purely Competitive Industry,then in the Long

If firms enter a purely competitive industry,then in the long run this change will shift the industry:

A) demand curve to the left,and the market price will decrease.
B) demand curve to the right,and the market price will increase.
C) supply curve to the right,and the market price will decrease.
D) supply curve to the left,and the market price will increase.