All of the options you listed represent aspects of product service management. Specifically:
A. Developing a new product - This is a key component of product management, as it involves creating and bringing new products to market.
B. Determining the cost of a new product - This is essential for budgeting, pricing strategy, and profitability analysis in product service management.
C. Changing a product like adding a new flavor - This represents product modification or line extension, which is part of managing a product's lifecycle.
D. Adjusting sale prices to meet customers' demand - Pricing strategies are crucial in product management to respond to market conditions and consumer behavior.
Therefore, all options (A, B, C, and D) represent elements of product service management.