optgroup の一部のアイテムを無効にするにはどうすればよいですか
「--ピックアップ--」と「--すべての場所--」を無効にしたい
<select name="ddlpickuplocation" id="ddlpickuplocation" tabindex="1" class="width320">
<optgroup label="california">
<option value="--Pick Up--">--Pick Up--</option>
<option value="LOS ANGELES AIRPORT (LAX)">LOS ANGELES AIRPORT (LAX)</option>
<option value="SAN DIEGO AIRPORT (SAN)">SAN DIEGO AIRPORT (SAN)</option>
<option value="SAN FRANCISCO AIRPORT (SFO)">SAN FRANCISCO AIRPORT (SFO)</option>
<option value="--All locations--">--All locations--</option>
<option value="ANAHEIM DOWNTOWN">ANAHEIM DOWNTOWN</option>
<option value="BATON ROUGE INTERNATIONAL AIRPORT">BATON ROUGE INTERNATIONAL AIRPORT</option>
<option value="BERKELEY DOWNTOWN">BERKELEY DOWNTOWN</option>
<option value="SAN JOSE AIRPORT">SAN JOSE AIRPORT</option>
<option value="SANTA BARBARA AIRPORT">SANTA BARBARA AIRPORT</option>
</optgroup>
<optgroup label="florida">
<option value="BOCA RATON AIRPORT">BOCA RATON AIRPORT</option>
<option value="CLEARWATER AIRPORT">CLEARWATER AIRPORT</option>
<option value="DAYTONA AIRPORT">DAYTONA AIRPORT</option>
</optgroup>
</optgroup>
<optgroup label="rest of usa">
<option value="--Pick Up--">--Pick Up--</option>
<option value="CHICAGO OHARE AIRPORT (ORD)">CHICAGO OHARE AIRPORT (ORD)</option>
<option value="--All locations--">--All locations--</option>
<option value="AKRON AIRPORT">AKRON AIRPORT</option>
<option value="ALLENTOWN AIRPORT">ALLENTOWN AIRPORT</option>
<option value="ALLENTOWN DOWNTOWN">ALLENTOWN DOWNTOWN</option>
<option value="AMARILLO AIRPORT">AMARILLO AIRPORT</option>
<option value="ANCHORAGE AIRPORT">ANCHORAGE AIRPORT</option>
<option value="ANDERSON DOWNTOWN">ANDERSON DOWNTOWN</option>
<option value="APPLETON AIRPORT">APPLETON AIRPORT</option>
<option value="ARKANUS AIRPORT">ARKANUS AIRPORT</option>
<option value="ATLANTA AIRPORT">ATLANTA AIRPORT</option>
</optgroup>
<optgroup label="western usa">
<option value="ALBUQUERQUE AIRPORT">ALBUQUERQUE AIRPORT</option>
<option value="ASPEN AIRPORT">ASPEN AIRPORT</option>
</optgroup>