单项选择题 A Company.com developer is designing a multi-tier web application and discovers a need to hide the details of establishing and maintaining remote communications from the client. In addition， because the business and resource tiers are distributed， the application needs to minimize the inter-tier network traffic related to servicing client requests.  Which design patterns， working together， address these issues？（）

单项选择题 A Company.com developer is designing the presentation tier for a web application that relies on a complex session bean. The session bean is still being developed and the APIs for are NOT finalized. Any changes to the session bean API directly impacts the development of the presentation tier.  Which design pattern provides a means to manage the uncertainty in the API？（）

多项选择题 A Company.com developer chooses to avoid using SingleThreadModel but wants to ensure that data is updated in a thread-safe manner.  Which two can support this design goal？（）