[Multiple-Choice Quiz Game] How to change the text quiz answer in the button into image?

I want to make a simple multiple choice quiz game with the coding below, but I want to make the multiple choice answers as image and the answer key too, so the right answer will be corrected with the same image, what should I change on the script ? Maybe any other opinion to make the multiple choice answers are image and the answer key (right answer). I'm new to Unity3D, and I'm sorry for my bad English.

     private int idLevel;
     public Text quest;
     public Text answerA;
     public Text answerB;
     public Text answerC;
     public Text answerD;
     public Text infoAnswer;
     public string[] dbQuest;
     public string[] dbAnswerA;
     public string[] dbAnswerB;
     public string[] dbAnswerC;
     public string[] dbAnswerD;
     public string[] trueAnswer;
     private int idQuest;
     private float answer;
     private float question;
     private float media;
     private int infoLevel;
     void Start () {
         idLevel = PlayerPrefs.GetInt ("idLevel");
         idQuest = 0 ;
         question = dbQuest.Length;
 
         quest.text = dbQuest [idQuest];
         answerA.text = dbAnswerA [idQuest];
         answerB.text = dbAnswerB [idQuest];
         answerC.text = dbAnswerC [idQuest];
         answerD.text = dbAnswerD [idQuest];
 
         infoAnswer.text = "question "+(idQuest + 1).ToString()+" from "+question.ToString()+"";
     }
     public void answ(string dbAnswer)
     {
         if(dbAnswer == "A"){
             if(dbAnswerA[idQuest] == trueAnswer[idQuest]){
                 answer += 1;
             }
         }
         else if(dbAnswer == "B"){
             if(dbAnswerB[idQuest] == trueAnswer[idQuest]){
                 answer += 1;
             }
         }
         else if(dbAnswer == "C"){
             if(dbAnswerC[idQuest] == trueAnswer[idQuest]){
                 answer += 1;
             }
         }
         else if(dbAnswer == "D"){
             if(dbAnswerD[idQuest] == trueAnswer[idQuest]){
                 answer += 1;
             }
         }
         nextQuestion();
     }
 
     void  nextQuestion(){
         idQuest += 1;
         if (idQuest <= (question - 1)) {
                 
         quest.text = dbQuest [idQuest];
         answerA.text = dbAnswerA [idQuest];
         answerB.text = dbAnswerB [idQuest];
         answerC.text = dbAnswerC [idQuest];
         answerD.text = dbAnswerD [idQuest];
         
         ....