前辈，我作为javascript新手在使用jquery的时候遇到了个问题，又不会百度搜，还望指教！

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

<script src="jquery.js"></script>

<script>

$(function(){

	$(".picture").hover(function(){

		$(this).addClass("pictureNew");

		},function(){

	    $(this).removeClass("pictureNew");

		})

})



$(document).ready(function(){

    var $cr=$("#checkbox");

	var cr=$cr[0];

	$cr.click(function(){

	   if($cr.is(":checkd")){

	      alert("Thank you for your cooperation!");

	   }

	})

})

</script>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

<title>login</title>

<link href="login.css" rel="stylesheet" type="text/css" />

</head>



<body>

<div class="login-box">

	<div class="head">

    10秒注册，获得<span class="height">高薪</span>

    </div>

    

    <ul class="containt">

    	<li class="email-box">

        邮箱 

        <input class="email" type="email">

        </li>

        

        <li class="password-box">

        密码 

        <input class="password" style=type"password">

        </li>

        

        <li class="password2-box">

        确认密码 

        <input class="password2" style=type"password">

        </li>

        

        <li class="test-box">

        验证码 

        <input class="test" type="text">  

        验证码图片  

        <a href="">换一张</a>

        </li>

        

        <li class="reading">

        <input class="checkbox" type="checkbox">

        我已阅读并同意<a class="book" href="">《**网用户协议书》</a>

        </li>

        

        <li class="picture-box">

        <a href=""><div class="picture"></div></a>

        </li>

    </ul>

    

    <div class="foot">

   	 <div class="number">已有账号？请<a href="">直接登录>></a></div>

    </div>

</div>

</body>

</html>