Javascript o无。：-） <form method="POST"> <table cellspacing="2" cellpadding="2"> <tr> <td valign

o无。：-）

<form method="POST">
    <table cellspacing="2" cellpadding="2">
        <tr>
            <td valign="top" /><b>Business:</b>
        <td><select id="business" name="business" >
            <option value="1">Sell</option>
            <option value="2">Buy</option>
            <option value="3">Both</option>
            <option value="4">Trade</option>
            <option value="5">Freight</option>
            <option value="6">Customs</option>
            </select>
        </td>
        </tr>    

        <div id="freight">
        <tr>
            <td><b>Service Type:</b></td>
        <td><select name="type">
            <option value="1">Air Cargo</option>
            <option value="2">Couriers</option>
            <option value="3">Freight Forwarder</option>
            </select>
            </td>   
        </tr>
        <tr>
            <td><b>Tollfree Number:</b></td>
            <td><input type="text" name="tollfree" />
            </td>
        </tr>
        </div>
                <tr>
                    <td valign="top"><b>Your Email Address:</b></td>
            <td><input type="text" name="email" /></td>
                    </tr>
    <div id="customs">
    <tr>
        <td /><b>Services:</b>
        <td>
            <input type="checkbox" value="ACA - Air Cargo Agent" />ACA - Air Cargo Agent<br /> 
            <input type="checkbox" value="AFF - Air Freight Forwarder" />AFF - Air Freight Forwarder<br /> 
        </td>
    </tr>
    </div>
            <tr>
            <td><b>Products/Services:</b></td>
            <td><input type="text" name="products" /></td>
            </tr>   
    <div id="brand">
        <tr>
            <td><b>Brand Names:</b></td>
            <td><input type="text" name="brands" /></td>
        </tr>
    </div>
    </table>
</form>

$(':checkbox').click(function() {
    $('input[name=products]').val(
        $(':checkbox:checked').map(function() {
            return $(this).val();
        }).get().join(',')
    );
});
$(document).ready(function () {
    toggleFields(); 
    $("#business").change(function () {
        toggleFields();
    });

});
function toggleFields() {
    if ($("#business").val() == 1 || ($("#business").val() == 2 || ($("#business").val() == 3)
        $("#brand").show();
        $("#freight").hide();
        $("#customs").hide();
    else
        if ($("#business").val() == 5)
            $("#brand").hide();
            $("#freight").show();
            $("#customs").show();
        else
            if ($("#business").val() == 6)
                $("#brand").hide();
                $("#freight").hide();
                $("#customs").show();   
            else
                $("#brand").hide();
                $("#freight").hide();
                $("#customs").hide();               
}

<tr id="freight">
    ...
</tr>

<div id="freight">
    <tr>
        ...
    </tr>
</div>