I have a form.

I use post method this form and backend is PHP.

<div class="form">
            <form action="" method="post" class="mt-2">
                <div class="form-group">
                    <select class="form-control" name="ra" onchange="xx()">
<!--                        <option value="a">a</option>-->
                        <option value="b">b</option>

When I select a or b I can post. It is work but my problem is when I selected b system works according to b but select default show a.

I want to show b or c.