Questions: Which system is used by management to perform "what-if" analysis to set optimal stock levels by store and warehouse?

The answer is the fourth one (D): Decision support system.

Explanation for each option:

1. Management information system (MIS): This system is primarily used for managing and processing data to produce reports that help in decision-making. However, it is not specifically designed for "what-if" analysis or setting optimal stock levels.

2. Transaction processing system (TPS): This system is used for handling day-to-day transactions and operations, such as sales, inventory, and payroll. It is not typically used for performing "what-if" analysis.

3. Executive support system (ESS): This system is designed to help senior executives make strategic decisions by providing easy access to internal and external information. While it supports decision-making, it is not specifically focused on "what-if" analysis for stock levels.

4. Decision support system (DSS): This system is specifically designed to support complex decision-making and problem-solving. It allows management to perform "what-if" analysis by simulating different scenarios to determine optimal stock levels by store and warehouse.

In summary, the Decision Support System (DSS) is the most appropriate choice for performing "what-if" analysis to set optimal stock levels.