SELECT-optgroup-label効果

<select name='Grade' class='s8'>
<option value=''>—   —</option>
<optgroup label=' '></optgroup>
<option value='18'>&nbsp;&nbsp; </option>

<optgroup label=' '></optgroup>
<option value='5'>&nbsp;&nbsp;1 </option>
<option value='6'>&nbsp;&nbsp;2 </option>
<option value='7'>&nbsp;&nbsp;3 </option>
<option value='8'>&nbsp;&nbsp;4 </option>
<option value='9'>&nbsp;&nbsp;5 </option>
<option value='10'>&nbsp;&nbsp;6 </option>

<optgroup label=' '></optgroup>
<option value='11'>&nbsp;&nbsp;7 </option>
<option value='12'>&nbsp;&nbsp;8 </option>
<option value='13'>&nbsp;&nbsp;9 </option>

<optgroup label=' '></optgroup>
<option value='14'>&nbsp;&nbsp;10 </option>
<option value='15'>&nbsp;&nbsp;11 </option>
<option value='16'>&nbsp;&nbsp;12 </option>
</select>