class Dog{ public String name; Dog(String name){ this.name =name; } } public class Demo1{ public static void main(String[] args){ Dog dog1 = new Dog("xiaohuang"); Dog dog2 = new Dog("xiaohuang"); String s1 = dog1.toString(); String s2 = dog2.toString(); String s3 = "xiaohuang"; String s4 = "xiaohuang"; } } A. dog1.equals(dog2) B. s1.equals(s2) C. s3.equals(s4) D. dog1==dog2