A monopoly firm is different from a perfectly competitive firm in that
A) there are many substitutes for the monopolist's product,whereas there are no close substitutes for the perfectly competitive firm's product. B) the monopolist's demand curve is perfectly inelastic,whereas the perfectly competitive firm's demand curve is perfectly elastic. C) the monopolist can influence price in the market,whereas the perfectly competitive firm is a price taker. D) All of these choices are true.