It is desirable that a certain method within a certain class can only be accessed by classes that are defined within the same package as the class of the method. How can such restrictions be enforced？（）  

• A、Mark the method with the keyword public.
• B、Mark the method with the keyword protected.
• C、Mark the method with the keyword private.
• D、Mark the method with the keyword package.
• E、Do not mark the method with any accessibility modifiers.