可以清除选择（即，选择第一个选项），像这样：

  $（＃primary_company）找到（'选项：第一'）
                     .attr（'选择'，'选择'）;
 

I have a set of radio buttons. When primary is selected, the Primary Company field is hidden. I would also like to at this time clear the drop down selection. How can I do this?

<p>
        <label>Company Type:</label>
        <label for="primary"><input onclick="javascript: $('#sec').hide('slow');" type="radio" runat="server" name="companyType" id="primary" checked />Primary</label>
        <label for="secondary"><input onclick="javascript: $('#sec').show('slow');" type="radio" runat="server" name="companyType" id="secondary" />Secondary</label>
        <div id="sec">
        <label for="primary_company">Primary Company:</label>
            <%= Html.DropDownList("primary_company", Model.SelectPrimaryCompanies, "** Select Primary Company **") %>
        </div>

    </p>

You can clear the selection (that is, select the first option) like so:

$("#primary_company").find('option:first')
                     .attr('selected','selected');