javascript菜单导航

<table cellspacing="0" cellpadding="0" border="0" style="text-align: center;  100%;
                       padding: 0; margin: 0; list-style: none; font-size: 16px;">
                    <tr>
                        <td>
                            <img src="images/li.jpg" alt="" />&nbsp;&nbsp;&nbsp;
                            <a class="menuParent" onclick="javascript:expand(1)"
                               href="javascript:void(0);">业务查询</a>
                        </td>
                    </tr>
                </table>
                <table id="child1" style=" text-align: center;  100%; padding: 0;
                       margin: 0; font-size: 13px;display:none;">
                    <tr style="height: 50">
                        <td>
                            &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<img src="images/li.jpg" alt="" />&nbsp;&nbsp;&nbsp;
                            <a class="menuChild" target="main"
                               href="QueryBusiness.aspx">注册号查询</a>
                        </td>
                    </tr>
                    <tr style="height: 50">
                        <td>
                            &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<img src="images/li.jpg" alt="" />&nbsp;&nbsp;&nbsp;
                            <a class="menuChild" target="main"
                               href="QueryoffNum.aspx">注销号查询</a>
                        </td>
                    </tr>
                </table>

 <script type="text/javascript" language="javascript">

            function expand(el) {
                childObj = document.getElementById("child" + el);
                if (childObj.style.display == 'none') {
                    childObj.style.display = 'block';
                }
                else {
                    childObj.style.display = 'none';
                }
                return;
            }
        </script>

 .menu_son { display: none; text-align: center; }