单项选择题 A developer is designing a multi-tier web application and discovers a need to hide the details of establishingand maintaining remote communications from the client. In addition， the application needs to find，in a transparent manner，the heterogeneous business components used to service the client’s requests. Which design patterns， working together， address these issues？（）

多项选择题 A developer has created a web application that includes a servlet for each use case in the application.These servlets have become rather difficult to maintain because the request processing methods havebecome very large. There is also common processing code in many servlets because these use cases arevery similar. Which two design patterns can be used together to refactor and simplify this web application？（）

多项选择题 You need to store a floating point number，called Tsquare，in the session scope. Which two code snippetsallow you to retrieve this value？（）