阅读下面的程序,正确的选项为() class Person{ String name; String nickName; public Person(String s,String t){ name = s; nickName = t; } public String toString(){ return name+" nickname="+nickName; } } public class Teacher extends Person{ String rank; public Teacher(String s,String t,String r){ super(s,t); rank=r; } public String toString(){ return name+" nickname="+nickName+" rank="+rank; } public static void main(String args[]){ Person a= new Person("Tom","Tiger"); Person b= new Teacher("Jack","Horse","Professor"); Teacher c= new Teacher("Bobby","Elephant","Lecturer"); System.out.println("a is "+a.toString()); System.out.println("b is "+b.toString()); System.out.println("c is "+c.toString()); } }