The Dividend Discount Model is a quantitative method of valuing a companys stock price based on the assumption that the the current fair price of a stock equals the sum of all of the companys future dividends discounted back to their present value. Therefore, an increase in which of the following will increase the current value of a stock according to the dividend growth model?

a. Both the discount rate and the dividend growth rate

b. Yield rate

c. Dividend growth rate

d. Discount on sales rate

e. All of the above