Scripts don't work when i try app

I am doing an application for android. When i start the game on Unity, or i try play on it all script and icons are working, but when i build my app and try it on my phone 2 botton don’t work (the button for exit game and the button for return to main menu). Help me please

N.B the button for return to main menu is in 2 scenes, in one is working, in the other no.

That are the scripts
Quit:

using UnityEngine;
using System.Collections;

public class Quit : MonoBehaviour {
	
	// Use this for initialization
	void Start () {
		
	}
	
	// Update is called once per frame
	void Update () {
		
	}
	void OnMouseDown() {
		Application.Quit();
	}
}

Main menù

using UnityEngine;
using System.Collections;

public class MainMenu : MonoBehaviour {


	// Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
	
	}
	void OnMouseDown() {
		if (GameObject.Find("?")!=null){
			GameObject.Find("?").audio.Stop();}
		Application.LoadLevel(0);

	}
}

OnMouseDown functions don’t work on iOS or Android. You need to use the Input class, see here:

I re-do the icon and now all work, I don’t change script