Which of the following statements about type compatibility is true?
an object of a subclass can be assigned to a reference to its superclass without a type cast

assigning an object of a superclass to a reference to one of its subclasses always causes a compilation error whether type casting is used or not

an object of a subclass can be assigned to a reference to its superclass, but type casting is required

an object of a superclass can be assigned to a reference to one of its subclasses without casting