是否有允许继承类修改c#中父类成员的访问修饰符?

class a
{
    int p  //should be accessable by b,c, but not by x
}

class b:a
{
    int q //should be accessable by c, if it has to by a, but not by x
}

class c:b
{
    public int r //obviously accessable by anyone
}

class x
{
    c testfunction()
    {
        c foo=new c();
        foo.r=20;
        return foo;
    }
}

这比这里的示例代码要复杂一点,但我想我已经把我的问题讲清楚了。