The fundamental System.Object base class and how its Equals method is used and overridden
String Handling, string builder, and how strings are concatenated
Regular Expressions - classes and methods for implementing fast, complex string searches
Groups of Objects - Arrays, Array Lists, Collections, and Dictionaries
Groups of Objects: Collection enumerator class
Groups of Objects: Dictionaries
Reflection - classes that assign attributes to code that can be queried at build and at run time
Threading - starting multiple execution threads, prioritorizing and synchronizing