The market for soccer balls is composed by 4 firms. Consider the following information on the quatity supplied at different prices: When the price for a ball is $25, the supply of firm 1 is 5, the supply of firm 2 is 2, the supply of firm 3 is 3, and the supply of firm 4 is 0. When the price for a ball is $50, the supply of firm 1 is 7, the supply of firm 2 is 5, the supply of firm 3 is 5, and the supply of firm 4 is 3. When the price for a ball is $75, the supply of firm 1 is 9, the supply of firm 2 is 8, the supply of firm 3 is 7, and the supply of firm 4 is 6. When the price for a ball is $100, the supply of firm 1 is 11, the supply of firm 2 is 11, the supply of firm 3 is 10, and the supply of firm 4 is 9. The slope of the market supply function, considering only the information provided above, is: a. Positive. b. Negative. c. Constant. d. Zero