You are building an Azure Durable Function that orchestrates an online ordering workflow and must call an external API to obtain product discount data. Which Durable Function types should you use?

The Orchestrator function defines the workflow logic, including how to call other functions and handle their outputs. It's responsible for the overall flow of the online ordering process. The Activity function performs the actual work, such as calling an external API to get product discount data. Orchestrator functions cannot directly call external APIs or perform I/O; they delegate these tasks to Activity functions. Entity functions are used for managing state and are not directly involved in orchestrating a workflow or calling external APIs for data. Client functions are used to start and manage Durable Function orchestrations, not to define the workflow or perform tasks within it.