鼠标移动Textbox上时，怎么全部选择TextBox的内容

鼠标移动Textbox上时，如何全部选择TextBox的内容？
鼠标移动Textbox上时，如何全部选择TextBox的内容？

 <tr>
                                                        <td align="right" bgcolor="#ffffff" width="20%">
                                                            外输：
                                                        </td>
                                                        <td bgcolor="#ffffff" width="180px">
                                                            <asp:TextBox ID="TextBox2" CssClass="text11" runat="server" Width="230px"></asp:TextBox>
                                                        </td>
                                                        <td align="right" bgcolor="#ffffff" width="10%">
                                                            温度：
                                                        </td>
                                                        <td bgcolor="#ffffff" width="180px">
                                                            <asp:TextBox ID="TextBox3" runat="server" Width="230px" CssClass="text11"></asp:TextBox> 
 
                                                        </td>
                                                    </tr>