表格嵌套,嵌套在里面的表格的上边框为什么不能外面的表格上边框对齐

                        </td>
                       <td background="http://i3.download.fd.pchome.net//g1/M00/08/15/ooYBAFOZAj-ISbS5AAGHYMA0yTQAABmMgJ5GAcAAYd4079.jpg">
                     <table border=1 width=550px height="245px" bgcolor="#999999" valign="top">
                       <tr valign="top">
                       <td>模块1</td>
                       <td rowspan=2 align="left" >模块3</td>
                       </tr>
                       <tr>
                       <td>模块2</td>

                       </tr>
                     </table>
                       </td>
                    </tr>
                    <tr>
                      <td height=30px colspan=2 align="center">版权声明</td>
                    </tr>
             </table>