A Button is positioned in a Frame. Only height of the Button is affected by the Frame while the width is not. Which layout manager should be used？（）    

class Parent {    
String one， two； 
public Parent（String a， String b）{    
one = a；    
two = b；    } 
public void print（）{ System.out.println（one）； }    } 
public class Child extends Parent {    
public Child（String a， String b）{    
super（a，b）；    
} 
public void print（）{ 
System.out.println（one + " to " + two）；    
} 
public static void main（String arg[]）{   
 Parent p = new Parent（"south"， "north"）；    
Parent t = new Child（"east"， "west"）；    
p.print（）；    
t.print（）；    
}    
} 
Which of the following is correct？（）

public class Parent {    
int change（） {…}    
} 
class Child extends Parent { 
   } 
Which methods can be added into class Child？（）