为什么鼠标滑过li都没加上样式，头痛欲裂~求救大神~~

Question

window.onload=function()
{
        var oTab=document.getElementById("month_tit");
        var oTac=document.getElementById("month_con");
        var aH3=oTab.getElementsByTagName("li");
        var aDiv=oTac.getElementsByTagName("div");
        for(var i=0;i<aH3.length;i++)
        {
                aH3[i].id=i;
                aH3[i].onmouseover=function()
                {
                        for (var j=0;j<aH3.length;j++)
                        {
                                aH3[j].className="";
                                aDiv[j].style.display="none";
                        }
                        this.className="select";
                        aDiv[this.id].style.display="block";
                }
        }
}

Answer 1

<div class="exam"> <div class="bannerright_top"> <span class="examdate">考试日历</span> <div class="month" id="month"> <div class="month_tit flexslider" id="month_tit"> <ul class="monthdate slides"> <li class="select"><span>1</span>月</li> <li><span>11</span>月</li> <li><span>12</span>月</li> </ul> </div> <div class="month_con" id="month_con"> <div class="mod" style="display:block;" id="mod"> <ul id="div1"> <li>计算机科学与应用<span>12月25日</span></li> <li>计算机科学与应用<span>12月25日</span></li> </ul> </div> <div class="mod" id="mod" style="display:none;"> <ul id="div1"> <li>计算机科学与应用<span>12月25日</span></li> <li>计算机科学与应用<span>12月25日</span></li> </ul> </div> </div> </div>

Answer 2

把你的html也粘出来，不然无从下手啊