一个简单的功能，应该不难实现，请大家帮帮我

Question

<script>
function showhide(which){
if( which.style.display=="none"){
which.style.display=""
}else{
which.style.display="none"
}
}
</script>
<table width="80%" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td bgcolor="#666666" onclick="showhide(content1)" style="color:white;cursor:hand">open1</td>
  </tr>
  <tr id="content1" style="display:none">
    <td>content1</td>
  </tr>
  <tr>
    <td bgcolor="#999999" onclick="showhide(content2)" style="color:white;cursor:hand">open2</td>
  </tr>
  <tr id="content2" style="display:none">
    <td>content2</td>
  </tr>
</table>