Which change can you make to Target without affecting Client?

Given:
1. public class Target {
2. private int i = 0;
3. public int addOne(){
4. return ++i;
5. }
6. }
And:
1. public class Client {
2. public static void main(String[] args){
3. System.out.println(new Target().addOne());
4. }

5. }
Which change can you make to Target without affecting Client?

A.
Line 2 of class Target can be changed to private Integer i = 0;

B.
Line 2 of class Target can be changed to private int i = 1;

C.
Line 4 of class Target can be changed to return i++;

D.
Line 3 of class Target can be changed to private int addOne(){