In a Perfectly Competitive Market, the Type of Decision a Firm

In a perfectly competitive market, the type of decision a firm has to make is different in the short run than in the long run. Which of the following is an example of a perfectly competitive firm's short-run decision?

A) Whether or not to enter or exit an industry.
B) What price to charge buyers for the product.
C) Whether or not to change its plant size.
D) How much to spend on advertising and sales promotion.
E) The profit-maximising level of output.