// menu switch
// id is the number of main menu
	function menu_nav(num){
		for(var id = 0;id<=6;id++)
		{
			if(id==num)
			{
				document.getElementById("qh_con"+id).style.display="block";
				document.getElementById("mynav"+id).className="nav_on";
			}
			else
			{
				document.getElementById("qh_con"+id).style.display="none";
				document.getElementById("mynav"+id).className="";
			}
		}
	}