jquery如何复制选定的行？

以下代码添加行只能复制第一行，如何复制选定的行？
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
 <HEAD>
  <TITLE> New Document </TITLE>
  <META NAME="Generator" CONTENT="EditPlus">
  <META NAME="Author" CONTENT="">
  <META NAME="Keywords" CONTENT="">
  <META NAME="Description" CONTENT="">
  <script type="text/javascript" language="javascript" src="jquery.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            //隐藏模板tr
            //$("#tb tr").eq(2).hide();
            var i = 1;
            $("#BtAdd").click(function () {
                //复制一行
                var tr = $("#tb tr").eq(1).clone();
                tr.find("td").get(0).innerHTML = ++i;
                var inputs = tr.get(0).getElementsByTagName("input");
                for(var j = 0 ; j < inputs.length; j ++)
                {
                    inputs[j].name = inputs[j].name+(i-1)
                    alert(inputs[j].name);
                }
                tr.show();
                tr.appendTo("#tb");
            });
            $("#BtDel").click(function () {
                $("#tb tr:gt(1)").each(function () {
                    if ($(this).find("#CK").get(0).checked == true) {
                        $(this).remove();
                    }
                });
                i = 1;
                $("#tb tr:gt(1)").each(function () {
                    $(this).find("td").get(0).innerHTML = ++i;
                });
                $("#CKA").attr("checked", false);
            });
            $("#CKA").click(function () {
                $("#tb tr:gt(1)").each(function () {
                    $(this).find("#CK").get(0).checked = $("#CKA").get(0).checked;
                });
            });
        })
    </script>
 </HEAD> <BODY>
  <table border="1" id="tb">
                        <tr>
                        <td style="text-align: center"></td>
                        <td><input id="CKA" name="CKA" type="checkbox"/></td>
                        <td>网</td>                        </tr>
                        <tr>
                        <td style="text-align: center">1</td>
                        <td><input id="CK" type="checkbox" name="CK"/></td>
                        <td><INPUT class="INPUT" TYPE="text" NAME="qq"></td>
                        </tr>
                    </table>                    <td width="50%" align="center">
                            <input id="BtAdd" type="button" value="添加行" Class="Btn"/>&nbsp;
                            <input id="BtDel" type="button" value="删除行"  Class="Btn"/>
                        </td>
 </BODY>
</HTML>