Problems when i click the button it has no sound in unity 3d c# help me guys this is for my thesis project

using UnityEngine; using System.Collections;

public class MainMenu : MonoBehaviour {

 private delegate void MenuDelegate();
 
 public AudioClip click;
 private float screenHeight;
 private float screenWidth;
 private float buttonHeight;
 private float buttonWidth;
 //Variables End
 void Start ()
 {
     screenHeight = Screen.height;
     screenWidth = Screen.width;
     
     buttonHeight = screenHeight * 0.1f;
     buttonWidth = screenWidth * 0.5f;
     
     //here we set the menuFunction to point to the anyKey function, which is further down in the code
 
 }

 void OnGUI () {
             // Make a background box
             //GUI.Box (new Rect (Screen.width / 2 - 190, 100, 100, 100), "Menu");
     
             // Make the first button. If it is pressed, Application.Loadlevel (Beta World) will be executed
             GUI.backgroundColor = Color.green;
     if(GUI.Button(new Rect((screenWidth - buttonWidth) * 0.5f, screenHeight * 0.4f, buttonWidth, buttonHeight), "Choose Mode"))
         
     {
                     Application.LoadLevel ("gamemode");
                     audio.PlayOneShot (click);
         
             }
     
             // Make the second button.
             GUI.backgroundColor = Color.yellow;
     if(GUI.Button(new Rect((screenWidth - buttonWidth) * 0.5f, screenHeight * 0.5f, buttonWidth, buttonHeight), "Instruction"))
         
     {
                     Application.LoadLevel ("instruction");
                     audio.PlayOneShot (click);
             }
     
             //Exit Game button
     GUI.backgroundColor = Color.blue;
     if(GUI.Button(new Rect((screenWidth - buttonWidth) * 0.5f, screenHeight * 0.6f, buttonWidth, buttonHeight), "Option"))
         
     {

                     Application.LoadLevel ("option");
                     audio.PlayOneShot (click);
             }
     
             //Options button, Use variables
             GUI.backgroundColor = Color.red;
     if(GUI.Button(new Rect((screenWidth - buttonWidth) * 0.5f, screenHeight * 0.7f, buttonWidth, buttonHeight), "Top Score"))

     {
                     Application.LoadLevel ("score");
                     audio.PlayOneShot (click);
             }
     }

 }