This option specifies the class that contains the entry point to the program, if more than one class contains a Main method.
The type that contains the Main method.
If your compilation includes more than one type with a Main method, you can specify which type contains the Main method that you want to use as the entry point into the program.
This option is for use when compiling an .exe file.
To set this compiler option in the Visual Studio development environment
Open the project's Properties page.
Click the Application property page.
Modify the Startup object property.
To set this compiler option programmatically, see StartupObject.
t3.cs, specifying that the Main method will be found in
csc t2.cs t3.cs /main:Test2