A polymorphic reference variable can refer to either an object of their own class or an object of the subclasses inherited from its class. In order to determine the type that a polymorphic variable refers to, the decision is made

a)		by the programmer at the time the program is written
b)		by the compiler at compile time
c)		by the operating system when the program is loaded into memory
d)		by the Java run-time environment at run time
e)		by the user at run time