Inheritance, Task 2
-------------------

1)            +---------+
              |    C    |
              +---------+
               ^       ^
               |       |
               |       |
       +---------+    +---------+
       |    B    |    |    D    |
       +---------+    +---------+
            ^
            |
            |
       +---------+
       |    A    |
       +---------+


2) a) allowed, because A is a subclass of B.
   b) not allowed, because C is not a subclass of B, it is its superclass.
   c) allowed, because A is a subclass of C.
   d) not allowed, because B is not a subclass of A, it is its superclass.
   e) not allowed, because B is not a subclass of D. They are both 
      direct subclasses of C.