A. class Bird implements Flyable { void fly() { System.out.println("鸟在飞"); } }

B. class Bird implements Flyable { public void fly() { System.out.println("鸟在飞"); } }

C. class Bird extends Flyable { public void fly() { System.out.println("鸟在飞"); } }

D. class Bird implements Flyable { protected void fly() { System.out.println("鸟在飞"); } }