class Animal{ Animal getOne(){return new Animal();}} class Dog extends Animal{ //insert code here } class AnimalTest{ public static void main(String[] args){ Animal[] animal={ new Animal(), new Dog()}; for(Animal a:animal){ Animal x= a.getOne(); } } } 和代码: 3a.Dog getOne() { return new Dog();} 3b.Animal getOne() { return new Dog();} 第3行中插入的哪项编译且运行无异常?