The two most common ways to expose your application to an external system are to leverage the Pega API (B) and to create a web service with the Service wizard (D). The Pega API provides a set of out-of-the-box RESTful endpoints for performing operations within the Pega Platform. The Service wizard simplifies the creation of SOAP or REST services, enabling external systems to interact with Pega applications.Reference: Pega Community documentation on Pega API and Service wizard.