[RESOLVED] [2.0] make a variable only accessable by the class it is in?

[high6]

I have a class formatted like below

class MyDll
{
class A_SubClass
{
public string A = "Access Me";
public string B = "Access Me";
public string z = "Don't Access Me";
}
class B_SubClass
{
public string A = new A_SubClass().z;
}
}

I want to have it so when using the dll I can't access "z" but I can access "z" from "B_SubClass" inside the dll.