div 层无法隐藏

我的页面中有多个div   每个div都有id值...

刚开始的时候我给每个div 都加上了style="display:none" 但它们都不显示.后来我改为用onload来隐藏..

function hideall()
  {  
   for(i=0;i<document.getElementsByTagName("div").length;i++)
       {
     document.getElementsByTagName("div")[i].style.display="none";
    }
  
  }


这样也不行..

我不知道为什么了..

以下是源码...


<form action="admindatabase.asp?act=add&rid=<%=rid%>"><table width="400"><tbody id="addnewone">
<tr>
      <td height="24" style="background-color:#CCCCCC" align=center>试题题目:</td>
   <td height=24 style="background-color: #CCCCCC"><input type="text" name="question"><input type="hidden" name="qnum" value="<%=tihao%>"><input type=hidden name=rid value="<%=request("rid")%>"></td>
    </tr>
<tr>
      <td height="24" style="background-color: #CCCCCC" align=center>试题类型:</td>
   <td height=24 style="background-color: #CCCCCC"><input type="radio" name="thetype" value="单项选择题">单项选择题&nbsp;<input type="radio" name="thetype" value="多项选择题">多项选择题&nbsp;<input type="radio" name="thetype" value="简答题">简答题&nbsp;<input type="radio" name="thetype" value="填空题">填空题&nbsp;</td>
    </tr>


<div id="show100001" style="position:absolute;display:none">
<tr>
    <td height="24" style="background-color: #CCCCCC" align=center>可选择项</td>
    <td style="background-color: #CCCCCC">A&nbsp;<input type="text" name="optiona" class=iptbox><br>B&nbsp;<input type="text" name="optionb" class="iptbox"><br>C&nbsp;<input type="text" name="optionc" class="iptbox"><br>D&nbsp;<input type="text" name="optiond" class="iptbox"><br>E&nbsp;<input type="text" class="iptbox" name="optione"><br>F&nbsp;<input class="iptbox" type="text" name="optionf">
    </td>
  </tr>
  <tr>
     <td style="background-color: #CCCCCC" align=center>标准答案:</td>
  <td style="background-color: #CCCCCC"><input type=radio name=answer value=A>A&nbsp;<input type=radio name=answer value=B>B&nbsp;<input type=radio name=answer value=C>C&nbsp;<input type=radio name=answer value=D>D&nbsp;<input type=radio name=answer value=E>E&nbsp;<input type=radio name=answer value=F>F
  </td>
  </tr>
</div>

<div id="show100002" style="display:none">
  <tr>
    <td height="24" style="background-color: #CCCCCC" align=center>可选择项</td>
    <td style="background-color: #CCCCCC">A&nbsp;<input type="text" name="optiona" class=iptbox><br>B&nbsp;<input type="text" name="optionb" class="iptbox"><br>C&nbsp;<input type="text" name="optionc" class="iptbox"><br>D&nbsp;<input type="text" name="optiond" class="iptbox"><br>E&nbsp;<input type="text" class="iptbox" name="optione"><br>F&nbsp;<input class="iptbox" type="text" name="optionf">
    </td>
  </tr>
  <tr>
     <td style="background-color: #CCCCCC" align=center>标准答案:</td>
  <td style="background-color: #CCCCCC"><input type="checkbox" name="msanswer" value="A">A&nbsp;<input type="checkbox" name="msanswer" value="B">B&nbsp;<input type="checkbox" name="msanswer" value="C">C&nbsp;<input type="checkbox" name="msanswer" value="D">D&nbsp;<input type="checkbox" name="msanswer" value="E">E&nbsp;<input type="checkbox" name="msanswer" value="F">F
  </td>
  </tr>
</div>

<div id="show100003" style="display:none">
     <tr>
     <td style="background-color: #CCCCCC" align=center>标准答案:</td>
  <td style="background-color: #CCCCCC"><input type=text name=tkkeys id="tkkeys" class="iptbox"></td>
     </tr>
  
</div>
<div id="show100004" style="display:none">
     <tr>
     <td height="25" align=center style="background-color: #CCCCCC">标准答案:</td>
  <td style="background-color: #CCCCCC"><textarea name="keys" cols="30" rows="4" id="jdkeys" class="iptbox"></textarea></td>
     </tr>
  
</div>
<tr>
    <td bgcolor="#CCCCCC" colspan="2" align="center"><input type="submit" name="submit" value="添加题目">&nbsp;&nbsp;<input type=reset value=重置所有>
    </td>
    </tr>

</tbody></table></form>

document.getElementsByTagName("div") 對象在哪呢？你沒定義吧？？？？