今天按照网上的例子做练习，代码如下：
<html>
<head>
<link rel =stylesheet href = "http://www.baidu.com">
</head>
<body>
<center>
<form method =post >
<h3>
姓名：<input name = "姓名" type = text value = "<%=Request.QueryString["姓名"]%>">
类别：<select name = "类别" size = 1>
<%String [] values = {"物理","化学","英语"};
for(int i = 0;i < values.Length;i++)
{
%>
<option
<%if(Request.QueryString["类别"] == values[i])
{Response.Write("selected");}
%>>
<%=values[i]%>
</option>
<%}%>
</select>
</h3>
<input type =submit name = "查找" value = "查找">
<p>
<%if(Request.QueryString["查找"] != null)
{
%>
您好<%=Request.QueryString["姓名"]%>，您选择了：<%=Request.QueryString["类别"]%>
<%}%>
</form>
</center>
</body>
</html>
在运行时，Request.QueryString["查找"] 返回的值一直是null，不知道是什么原因
