<form method = "post">
<label for = "type">Тип</label>
<select id = "type" name = "type">
<option value = "B">B</option>
</select>
<input type = "submit" value = "Выбрать">
</form>
<?php
$type = $_POST['type'];
if ($type=='B')
{
echo "Выбрана запись типа B";
}
?>