*Async Feature ----Two new key words are used for Async feature: async modifier and await operator. Method marked with async modifier is called async method. This new feature will help us a lot in async programming. For example, in the programming of Winform, the UI thread will be blocked while we use HttpWebRequest synchronously request any resource in the Internet. From the perspective of user experience, we cannot interact with the form before the request is done. *Caller Information --Caller Information can help us in tracing, debugging and creating diagnose tools. It will help us to avoid duplicate codes which are generally invoked in many methods for same purpose, such as logging and tracing.