Which of the following is not true about declaring references to objects of other classes inside a class definition?

a. These references can be initialized inside the class definition.
b. Each reference only requires enough memory to store the memory address of the object it references.
c. If the class names for the other objects are used only to declare references, a forward declaration can be used to tell the compiler that the class name represents a type.
d. These references can represent directional associations from a UML class diagram.

a. These references can be initialized inside the class definition.