Which of the following best represents a firms sustainable growth rate?

a. None of the above

b. The maximum rate of growth in profits that a firm can achieve while maintaining its present stock price

c. The maximum rate of growth in stock price that a firm can achieve while maintaining its optimal debt structure

d. The maximum rate of growth in earnings per share that a firm can achieve while maintaining its optimal return on equity

e. The maximum rate of growth in sales that a firm can achieve while maintaining its present capital structure