A marketing firm decides to purchase media time in an attempt to sell its new product. After purchasing approximately $1 million dollars of time, it has noticed no impact on the sales of the product. However, at $3 million, a substantial increase is shown. This might best be explained by:
A. arbitrary allocation method.
B. the objective and task method.
C. competitive parity method.
D. an S-shaped response function.
E. rapidly diminishing returns.
Answer: D