在Wordpress中验证下拉表单

Question

我在下面使用WordPress提供此表单。我们有一个我们销售的产品，用户需要选择品牌和型号。我们遇到的问题是他们在没有选择品牌和型号的情况下提交表单。试着尽可能轻松地解决如何做到这一点，因为我没有编写代码，而且我的开发人员在行动中缺失。

如果不首先选择品牌和型号，我们如何确保他们无法提交？

谢谢。

<div class="span6">

    <script src="http://demosite.com/demp_data.js"></script><script src="http://demosite.com/helpers.js"></script>
    <h4>$88.99 (Discounts Available for Multiple Purchases)</h4>
    <img style="float: left; margin-right: 10px;" src="http://demosite.com/wp-content/uploads/2014/01/demo.gif" alt="" />
    <p style="line-height: 25px;">Demo Product is Made in the USA!</p>

    <div style="height: 10px;"></div>
    <img src="http://demosite.com/wp-content/uploads/2014/01/demo.jpg" alt="" />

</div>
<div class="span6">
    <div class="box1">
        <div class="striped"></div>
        <h6 class="fontbold"><i class="icon-truck"></i> Purchase Our Product</h6>
        <form action="https://www.paypal.com/cgi-bin/webscr" method="post">

            <input name="cmd" type="hidden" value="_s-xclick" /><input name="hosted_button_id" type="hidden" value="9VAWUWSFLS6SG" />
            <table style="border: 1px solid #fff; border-collapse: separate;">
                <tbody>
                <tr>
                    <td><input name="on0" type="hidden" value="Quantity" /><span class="green">Quantity</span></td>
                </tr>
                <tr>
                    <td><select name="os0"><option value="1 Test Product">1 Test Product $88.99 USD</option><option value="2 Test Productes">2 Test Productes $221.99 USD</option><option value="3 Test Productes">3 Test Productes $223.99     USD</option></select></td>
                </tr>
                <tr>
                    <td><input name="on1" type="hidden" value="Test Product make" /><span class="green">Test Product Make</span></td>
                </tr>
                <tr>
                    <td><select id="demo_names" name="os1"><option value="-1">Select a Test Product make</option></select></td>
                </tr>
                <tr>
                    <td><input name="on2" type="hidden" value="Test Product model" /><span class="green">Test Product Model</span></td>
                </tr>
                <tr>
                    <td><select id="demp_models" name="os2"><option>Select a Test Product model</option></select></td>
                </tr>
                <tr>
                    <td><input name="on3" type="hidden" value="Watt" /><input id="watt" name="os3" type="hidden" /><input alt="PayPal - The safer, easier way to pay online!" name="submit"     src="https://www.paypalobjects.com/en_US/i/btn/btn_buynowCC_LG.gif" type="image" /><img src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" alt="" width="1" height="1" border="0" />

                        Don't See Your Make and Model? <a title="Contact" href="http://www.ezTest Productswitch.com/contact/">Contact Us!</a>
                        <input name="on5" type="hidden" value="Notes" /><input id="notes" name="os5" type="hidden" /></td>
                </tr>
                <tr>
                    <td><input name="currency_code" type="hidden" value="USD" /></td>
                </tr>
                </tbody>
            </table>
        </form></div>
</div>