Question:Show the WF activity hierarchy. 

WF Activity: CodeActivity, AsyncCodeActivity, NativeActivity, And Dynamic Activity.

Question:What is the function of WCF? 

WCF Workflow Service applications are a new type of project in VS2010 that make it very easy to create workflows for sending and receiving data

Question:What is the usefulness of HTTP Caching? 

One of the biggest advantages to using Restful services is that you can take advantage of HTTP caching features to improve performance and reduce load on the service.

Question:what are the benefits of using EF (Entity framework)? 

EF (entity Framework) provides an abstraction above the database layer and a number of enhancements that make it superior to LINQ to SQL.