9.The following statements are about type-casting, which one is correct? A. A reference variable of a class can only be assigned to an object of its first level sub-classes of this class. B. An object can not be casted to the type of another class which has no inheritance relationship with the object’s original class. C. A child class’s reference variable can be assigned to an object of its parent class. D. There is only explicit casting, but no implicit casting.