A competitive firm has a long-run total cost function c(y) = 3y2 + 675 for y > 0 and c(0) = 0. Its long-run supply function is described as

a.y =if p > 90, y = 0 if p < 90.

b.y =if p > 88, y = 0 if p < 88.

c.y =if p > 93, y = 0 if p < 99.

d.y =if p > 93, y = 0 if p < 93.

e.y =if p > 95, y = 0 if p < 85.