why d wrongAnd why choose b

of b 14. In perfect competition, which statement is true? a. In the long run in a constant-cost industry, a firm has a perfectly elastic supply curve. b. In the long run in a constant-cost industry, firms have an upward sloping supply curve and the industry supply curve is perfectly elastic. c. In the long-run in a constant-cost industry, firms have an upward-sloping supply curve and face a downward sloping demand curve. d. In the long run in a constant cost industry, firms have an upward sloping supply curve and the industry supply curve is the horizontal summation of the supply curves of firms currently in the industry. e. In the long run in a constant cost industry, firms have a perfectly elastic supply curve and the long- run industry supply curve is horizontal