If S represents weekly sales of a product. What can be said of S' and S" for each of the following statements? 

(a) The rate of change of sales is increasing. 

(b) Sales are increasing at a slower rate. 

(c) The rate of change of sales is constant. 

(d) Sales are steady. 

(e) Sales are declining, but at a slower rate. 

(f) Sales have bottomed out and have started to rise.