The rule of MC = MR does not apply to a monopolist.

Tax Wedge

What will be an ideal response?

During the great canal-building era, from roughly 1815 to 1843, Hughes and Cain (2011) claim that

(a) most canals earned normal profits. (b) no canals earned profits. (c) all canals in the initial period of construction earned normal profits but none did in the later period because of over-construction and competition from the railroads. (d) the Erie Canal was one of the few, perhaps the only one, to earn normal profits.