Extension methods are available starting with C# 3.0 and Visual Basic 9.0, which were released in 2007 with version 3.5 of the .NET platform.
Type inference refers to the ability of a programming language to automatically deduce a variable’s type. The feature was added to C# and Visual Basic to support anonymous types and the relaxed programming style required by Linq.
Roger McCook offers you an overview of the new technology of Ajax.