帮我看段程序

<%@ Page Language="C#" %><html>
   <head>
      <link rel="stylesheet"href="intro.css">
   </head>   <body><!-- #include File="C:\Inetpub\wwwroot\DotNetJunkies\DotNetJunkiesWeb\_js\omni.inc" -->       <center>       <form action="intro3.aspx">           <h3> Name: <input name="Name" type=text value="<%=HttpUtility.HtmlEncode(Request.QueryString["Name"])%>">           Category:  <select name="Category" size=1>                         <%
                             String [] values = { "psychology", "business", "popular_comp" };                             for (int i=0; i<values.Length; i++) {
                          %>                                <option <% if (Request.QueryString["Category"] == values[i]) { Response.Write("selected"); } %>>
                                   <%=values[i]%>
                                </option>                          <% } %>                      </select>           </h3>           <input type=submit name="Lookup" value="Lookup">           <p>           <% if (Request.QueryString["Lookup"] != null) { %>              Hi <%=HttpUtility.HtmlEncode(Request.QueryString["Name"]) %>, you selected: <%=HttpUtility.HtmlEncode(Request.QueryString["Category"]) %>           <% } %>       </form>       </center>   </body>
</html>
点了提交以后，在地址栏就会有下面的地址http://localhost/test.aspx?Name=ppp&Category=psychology&Lookup=Lookup什么情况下，表单的提交会放到地址栏里面啊，并且不理解，为什么提交按钮也会在地址栏里面呢？？