Only one thing exists:
. "System" can be omitted if you used
Honestly, sometimes I think that the use of "using" clause should be prohibited to some beginners, to let them understand the basics. You probably don't understand what is the type name and how namespaces work. Better read on this topic:
You won't be able to do any reasonable software development if you don't understand this very basic and simple thing. I'm afraid to know what's next. How to use assemblies?