Ali wanted to figure out the selling price for the custom paperweights he planned to sell. He found that at a price of $5.00, he could sell 20 units; at a price of $10.00, he could sell 15 units; and at a price of $20.00, he could sell 5 units. Based on these numbers, how could Ali make the maximum profit?
A. sell at $5.00
B. sell only 15 units
C. sell at $10.00
D. sell less than 20 units
E. sell at $20.00