Why a function with protected modifier can be overridden and accessible every where?

I'm C# programmer new to D language. I'm a bit to confused with OOP in D programming language.

Assuming that I have the following class:

public class A {   protected void foo() {      writefln("A.foo() called.");   }};public class B : A {   public override void foo() {      writefln("B.foo() called.");   }};

The protected modifier means that I can access the .foo() method just on inherited class,so why this D program compiles normally?

Here is the equivalent to C#.NET:

using System;public class A {   protected virtual void foo() {      Console.WriteLine("a.foo() called.");   }};public class B : A {   public override void foo() {      Console.WriteLine("b.foo() called.");   }};public class MainClass  {   public static void Main(string[] args) {      A a = new A();      B b = new B();          a.foo();      b.foo();   }};

It don't compiles and given the following error message(as I expected):

test.cs(10,30): error CS0507: B.foo()': cannot change access modifiers when overridingprotected' inherited member `A.foo()'

Can someone explain this D behavior? Thanks in advance.