HTML class inheritance

    <ul class="subjects">
        <?php
        // 3. Use returned data ( if any )
        while($subject=mysqli_fetch_assoc($subject_set)){
            ?>
            <?php
                  echo "<li ";
                  if ($subject["id"]==$selected_subject_id){
                      echo "class=\"selected\"";
                  }

                  echo ">"
            ?>
                <a href="manage_content.php?subject=<?php echo urlencode($subject["id"])  ?>"><?php echo $subject["menu_name"]; ?></a>
                <?php
                    $page_set=find_all_pages_for_subject($subject["id"]);
                ?>
                <ul class="pages">
                    <?php
                     while($page=mysqli_fetch_assoc($page_set)){
                    ?>
                         <?php
                         echo "<li ";
                         if ($page["id"]==$selected_page_id){
                             echo "class=\"selected\"";
                         }

                         echo ">"
                         ?>
                        <a href="manage_content.php?page=<?php echo $page["id"] ?>"><?php echo $page["menu_name"];  ?></a>
                    </li>
                         <?php
                     }
                    ?>
                    <?php
                    //4. Release returned data
                    mysqli_free_result($page_set);
                    ?>
                </ul>
            </li>

            <?php
        }
        ?>
    </ul>

Piece of my stylesheet

ul.subjects { padding-left: 0; list-style: none;}

ul.pages { padding-left: 2em; list-style: square; font-weight: normal; }

.selected { font-weight: bold; }

Idea is to have bold only selected link, but when I click on subject link all my sub-links ( pages ) get class "selected" and remain bold. How to resolve that? ;)