var show1= "tz";
    var show2="szf";
    var show3= "sj";
    function showlist(obj,listno)
    {
     switch(listno){
     case 1:document.getElementById(show2).src="images/"+show2+"2.jpg";
            document.getElementById(show3).src="images/"+show3+"2.jpg";
            document.getElementById(show2+"list").style.display="none";
            document.getElementById(show3+"list").style.display="none";
            break;
            
     case 2:document.getElementById(show1).src="images/"+show1+"2.jpg";
            document.getElementById(show3).src="images/"+show3+"2.jpg";
            document.getElementById(show1+"list").style.display="none";
            document.getElementById(show3+"list").style.display="none";
            break;
            
     case 3:document.getElementById(show1).src="images/"+show1+"2.jpg";
            document.getElementById(show2).src="images/"+show2+"2.jpg";    
            document.getElementById(show1+"list").style.display="none";
            document.getElementById(show2+"list").style.display="none";
            break;      
            }
        var objname=obj.id;
        obj.src ="images/"+objname+"1.jpg";
        document.getElementById(objname+"list").style.display="";
    }