table 的rolspan和rowspan

如图所示啦，容易让初学者混乱的两个东西
仔细看看分析下呢，就比较简单了

<table width="300" border="2">
  <tr>
    <th scope="col"> th>
    <th scope="col"> th>
    <th scope="col"> th>
  tr>
  <tr>
    <td rowspan="2">1td>
    <td>2atd>
    <td>3atd>
  tr>
  <tr>
    <td>2td>
    <td>3td>
  tr>
  <tr>
    <td> td>
    <td colspan="2">4td>
  tr>
table>