在List.aspx写了个下拉列表如何在List.cs中获取下拉列表中的相应的选项

<b>企业类型<b>
                    <select name="gongcheng" id="ck_select" runat=server>
                     <option value="0" selected>请选择</option>
                     <option value="1">施工企业 </option>
                     <option value="2">监理企业</option>
                     <option value="3">设计企业</option>
                     <option value="4">勘察设计企业</option>  
                     </select>
                    &nbsp;&nbsp;&nbsp;&nbsp;
                    <asp:Button ID="Button2" runat="server" Text="查询"  OnClick="btnSelect_Click" >
                    </asp:Button>  

在List.cs文件中 怎么 获得 “施工企业” “监理企业”

用Request["gongcheng"]??