a supply curve slopes upward because
a.
â as more is produced, total cost of production falls.
b.
â many firms will experience increases in their costs of production as their output rises so they need a higher price in order to induce them to produce more output.
c.
â the higher the price per unit, the greater the profitability generated by supplying more of that good.
d.
â both (b) and (c).