请问我做的轮播图，为什么只轮播了一下，而且第二章上面还出现了一个小图标。
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>京东轮播图代码</title>
</head>
<body>
<div class="slider" id="circle" style="width:790px; height:340px; overflow:hidden;">
<a href="https://item.jd.com/11141344903.html#crumb-wrap" ><img src="images/zp (1).jpg" alt="" /></a>
<a href="http://xxbuyun.jd.com/"><img src="images/zp (2).jpg" styly="width:790px; height:340px" alt="" /></a>
<ul class="circle">
<!--移动鼠标触发事件-->
<li onmouseover="lunbo(1)" id="1" >1</li>
<li onmouseover="lunbo(2)" id="2">2</li>
</ul>
<div class="arrow">
<a href="javaScript:;" class="arrow-l" onclick="bo2()" id="bo1"></a>
<a href="javaScript:;" class="arrow-r" onclick="bo1()" id="bo2"></a>
</div>
</div>
<script>
var a = 1;
var t = 0;
window.onload = function(){
t = setInterval("bo1()", 2000);
}
function lunbo(num){
a = num;
var btn = document.getElementById("circle").getElementsByTagName("img")[0];
for (var i=1;i<3;i++) {
var li = document.getElementById("circle").getElementsByTagName("li")[i-1];
li.style.backgroundColor = "#3E3E3E";
if(num == i){
btn.src = "img/"+i+"p.jpg";
li.style.backgroundColor = "#B61B1F";
}
}
}
function bo1(){
if(a==2){
a = 1;
}
a++;
lunbo(a);
}
function bo2(){
if(a ==1){
a = 2;
}
a--;
lunbo(a);
}
</script>
</body>
</html>
