background

How to set a gray background for the first and third rows only? <table>     <tr>          <td>name</td>          <td>one</td>     </tr>      <tr>          <td>name</td>          <td>two</td>     </tr>      <tr>          <td>name</td>          <td>three</td>     </tr>      <tr>          <td>name</td>          <td>four</td>     </tr> </table>