如图，结果只显示出来四个。其实有好多，但是下拉列表里就显示出来4个。

code：

<asp:TextBox ID="txtJg" runat="server"></asp:TextBox>
            </td>
                <td class="style3"> &nbsp;民&nbsp;&nbsp;&nbsp;&nbsp;族<asp:TextBox ID="txtMz" runat="server"
                        ontextchanged="txtMz_TextChanged"></asp:TextBox>
                    <asp:Panel ID="Panel1" runat="server" ScrollBars="Vertical" Visible="false" Height="100px">  
                        <asp:GridView ID="GridView1" runat="server" AutoGenerateSelectButton="false"
                            onrowdatabound="GridView1_RowDataBound"
                            onselectedindexchanged="GridView1_SelectedIndexChanged"
                            onselectedindexchanging="GridView1_SelectedIndexChanging">
                            <Columns>
                                <asp:BoundField DataField="mz"/>
                            </Columns>
                        </asp:GridView>
                    </asp:Panel>
                <asp:DropDownExtender ID="DropDownExtender1" runat="server" TargetControlID="txtMz" DropDownControlID="Panel1">
                    </asp:DropDownExtender>