I would choose the third alternative (C).
The decrease in the demand for a company's products should be evaluated by different responsible management. What a marketing manager can do is seek alternative solutions to try to solve the problem. She needs to understand the reason for the drop in sales to develop a product advertisement that will restore the public's willingness to buy. That is, the marketing area is responsible for advertising the product and this often involves creative imagination.
Other areas may contribute differently. The production manager can analyze a specific product problem and the finance director can evaluate the feasibility of this product and its possible replacement.