The correct answer is: C. provide after-sales service.
Supplementary costs are costs that are incurred in addition to the direct costs of production. They are often referred to as indirect costs or overhead costs. Supplementary costs can include costs such as marketing, advertising, research and development, and customer service.
After-sales service is a type of supplementary cost that is incurred after the sale of a product or service. It can include costs such as providing technical support, repairing or replacing defective products, and providing refunds or exchanges.
After-sales service is important because it can help to improve customer satisfaction and loyalty. It can also help to reduce the number of returns and complaints. Additionally, after-sales service can help to generate positive word-of-mouth advertising and referrals.
The other options are incorrect because:
- Option A is incorrect because the demand curve is a function of consumer preferences, not production costs.
- Option B is incorrect because the per unit cost of production is determined by the production process, not by supplementary costs.
- Option D is incorrect because increasing returns to scale are a function of the production process, not by supplementary costs.