Answer:
d. A subclass reference can be assigned to a superclass variable, but a superclass reference cannot be assigned to a subclass variable.
Step-by-step explanation:
A subclass is a class which is derived from another class. A subclass will have the characteristics of its ancestor class. A superclass is a class which is class direct ancestor. A superclass is an existing class from which new classes are derived whereas subclass is a class which is derived from superclass. The correct statement is that a subclass can be assigned to a superclass variable.