求一段javascript程序，实现图片的交替显示

Question

<img border="0" src="movie1.png" width="350" height="250">  
<div>
  <img border="0" src="movie1.png" width="50" height="40">
  <img border="0" src="movie2.png" width="50" height="40">
  <img border="0" src="movie3.png" width="50" height="40">
</div>
要求：点击下面的小图片时，把其放大显示在大图片处（红色）
　　　且图片的最大尺寸不能超过350*250

Answer 1

<img id="largeImg" border="0" src="movie1.png" width="350" height="250"> 
<div> 
  <img onclick="a(this)" border="0" src="movie1.png" width="50" height="40"> 
  <img onclick="a(this)" border="0" src="movie2.png" width="50" height="40"> 
  <img border="0" src="movie3.png" width="50" height="40"> 
</div>
<script>
function a(obj)
{
 var src = obj.src;
 var largeImg = document.getElementById("largeImg");
 largeImg.src = src;
}
</script>

Answer 2

<img id="largeImg" border="0" src="movie1.png" width="350" height="250"> 
<div> 
  <img onclick="a(this)" border="0" src="movie1.png" width="50" height="40"> 
  <img onclick="a(this)" border="0" src="movie2.png" width="50" height="40"> 
  <img border="0" src="movie3.png" width="50" height="40"> 
</div> 
<script> 
function a(obj) 
{ 
var src = obj.src; 
var largeImg = document.getElementById("largeImg"); 
largeImg.src = src; 
} 
</script> 

Answer 3

<img id="largeImg" border="0" src="movie1.png" width="350" height="250"> 
<div> 
  <img onclick="a(this)" border="0" src="movie1.png" width="50" height="40"> 
  <img onclick="a(this)" border="0" src="movie2.png" width="50" height="40"> 
  <img onclick="a(this)" border="0" src="movie3.png" width="50" height="40"> 
</div> 
<script> 
function a(obj) 
{ 
var src = obj.src; 
var largeImg = document.getElementById("largeImg"); 
largeImg.src = src; 
largeImg.width=350;
largeImg.height=350/obj.width*obj.height;
} 
</script>