1.If a firm is making positive short run profit in a perfectly competitive market,what do you expect happens in the long run, and why?Read all answers and choose the most correct one.

a. Profit tends to zero -other firms enter market

b. Profits increase -firm gets more efficient over time

c. Profit stays the same -no incentive for other firms to enter

d. Profit stays the same - short run profit is sustainable long term