为什么用js生成单选框，IE浏览器无法选中

我用js动态生成的单选框，用firefox浏览可以使用，但是用IE浏览时却无法选中不知道为什么
这是我的代码
<html>
  <head>
    <base href="<%=basePath%>">
        <meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">

<script type="text/javascript">
window.onload = function()
   {
   for(var  i = 0;i < 3;i++)
{
                   var form = document.getElementById("form");
   var input = document.createElement("input");
   input.setAttribute("type","radio");
   input.setAttribute("name","answer");
    if(i == 0)
    {
input.setAttribute("checked",true);
     }
       form.appendChild(input);
}
        }

</script>
  </head>

  <body >
    <form id="form">

    </form>
  </body>
</html>

解决方案 »

免费领取超大流量手机卡，每月29元包185G流量+100分钟通话, 中国电信官方发货

<html>
  <head>
    <base href="<%=basePath%>">
        <meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">

<script type="text/javascript">
window.onload = function()
   {
   for(var  i = 0;i < 3;i++)
{                       var form = document.getElementById("form");
if(i == 0){    var input = document.createElement("<input type='radio' name='answer' checked>");
}else{
                   var input = document.createElement("<input type='radio' name='answer' >");
}

       form.appendChild(input);
}
        }

</script>
  </head>

  <body >
    <form id="form">

    </form>
  </body>
</html>