Which access modifier should you use to declare the new class?

You are C# developer who is developing a Windows application. You develop a new class that must be accessible to all the code packaged in the same assembly. Even the classes that are in the same assembly but do not directly or indirectly inherit from this class must be able to access the code. Any code outside the assembly should not be able to access the new class. Which access modifier should you use to declare the new class?
A. public
B. protected
C. private
D. internal