The include method defined in the RequestDispatcher class can be invoked even if response has been committed (unlike forward). include() does not throw an IllegalStateException even if the response was already committed. Hence B is incorrect.
a is not currect, as can be verified from the apis
Full path means context level path, or say it root level path that begins with "/".
Straight from Java� Servlet Specification Version 2.4
The getRequestDispatcher method takes a String argument describing a path within the scope of the ServletContext. This path must be relative to the root of the ServletContext and begin with a �/�.
To allow RequestDispatcher objects to be obtained using relative paths that are relative to the path of the current request (not relative to the root of the ServletContext), the getRequestDispatcher method is provided in the ServletRequest interface.