Given the following class and reference declarations, what can be said about the statement y = (Sub) x?

Select the one correct answer.

(a) It is illegal at compile time.

(b) It is legal at compile time, but might be illegal at runtime.

(c) It is definitely legal at runtime, but the cast operator (Sub) is not strictly needed.

(d) It is definitely legal at runtime, and the cast operator (Sub) is needed.

// Class declarations: class Super {} class Sub extends Super {} // Reference declarations: Super x = null; Sub y = null;