Public and Internal members in an Internal class?

Consider this case:

public interface IBar { void Bar(); }
internal class C : IBar
{
    public void Bar() { }
}

Here C.Bar cannot be marked as internal; doing so is an error because C.Bar can be accessed by a caller of D.GetBar():

public class D
{
    public static IBar GetBar() { return new C(); } 
}

A commenter asked a follow-up question: is an explicit implementation of an interface method considered to be public, or private? (C# does not allow you to put an access modifier on an explicit implementation.)

Take a step back and think about what exactly is "public" or "private" about a member: people think wrong things like "private means that a method cannot be called from outside the class", but that's not true; the class could make a delegate to a private method, pass it to anyone, and they can then call a private method.

Rather, accessibility determines where the name of a thing can be used! Explicit interface implementations do not add a name to the class declaration space in the first place; they can only be referred to by name via the interface, not the class. It really doesn't make sense to think of explicit interface implementations as public or private because they don't have a name you can refer to.

A public member is still just internal when in an internal class.

From MSDN:

The accessibility of a member can never be greater than the accessibility of its containing type. For example, a public method declared in an internal type has only internal accessibility

Think of it this way, I would access a public property on....? A class I can't see? :)

Eric's answer is very important in this case, if it's exposed via an interface and not directly it does make a difference, just depends if you're in that situation with the member you're dealing with.