1. public interface A { 
2. public void doSomething（String thing）； 
3. } 
1. public class AImpl implements A { 
2. public void doSomething（String msg） { } 
3. } 
1. public class B { 
2. public A doit（） { 
3. // more code here 
4. } 
5. 
6. public String execute（） {
7. // more code here 
8. } 
9. } 
1. public class C extends B { 
2. public AImpl doit（） {
 3. // more code here 
4. } 
5. 
6. public Object execute（） { 
7. // more code here 
8. } 
9. } 
Which statement is true about the classes and interfaces in the exhibit？（）