function switchMenu(curr_id, total_num) 
{
  	 for(var i=0; i<total_num; i++) 

    { 
        //二级菜单 

        var el = document.getElementById('menu_sub_'+i); 
        if(!el) return; 

        //一级菜单前面的图片
        var img = document.getElementById('menu_master_'+i); 

        if(i == curr_id) 

        { 
            el.style.display = "block"; 
            img.src = "images/-.gif"; 
        } 
        else 
        { 
            el.style.display = "none"; 
            img.src = "images/+.gif"; 
        } 
    } 
}