public class A1 {public A1() {System.out.println("hello");}}public class A2 extends A1 {public A2() {System.out.println("world");}}public class A3 extends A2 {public A3() {System.out.println("china");}}public class B {public static void main(String[] args) {A1 x = new A3();}}以上程序的输出结果是？
选项：

A:hello
B:helloworld2
C:helloworldchina
D:程序错误