Prevent source image change on click

I am creating a level as shown in below image where , when a button is clicked from group of buttons on the left and then any one of the 4 buttons on the right is clicked ,then the source image of the first clicked button will change to the image of the second clicked button . It works fine , but the problem is that when i try to do this on another button from the group previously selected button's source image will also change and all buttons will have same image . Is there a way where i can prevent change of source image of the button after click.

Code :

using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.UI;

public class ControlBtn : MonoBehaviour { public Button Question;

 public Button Answer1;
 public Button Answer2;
 public Button Answer3;
 public Button Answer4;

 public Sprite AnsImg1;
 public Sprite AnsImg2;
 public Sprite AnsImg3;
 public Sprite AnsImg4;


 public void ButtonClick()
 {
     Answer1.onClick.AddListener(ans1);
     Answer2.onClick.AddListener(ans2);
     Answer3.onClick.AddListener(ans3);
     Answer4.onClick.AddListener(ans4);
 }

 void ans1()
 {

     Question.GetComponent<Image>().sprite = AnsImg1;
     
 }
 void ans2()
 {
     Question.GetComponent<Image>().sprite = AnsImg2;
     
 }
 void ans3()
 {
     Question.GetComponent<Image>().sprite = AnsImg3;
     
 }
 void ans4()
 {
     Question.GetComponent<Image>().sprite = AnsImg4;
 }

}