Jquery 动态为table添加行

//新增试卷_添加行 
function addtr(id) {
    tr_id = $("#tQuestion>tbody>tr:last").attr("id");
    tr_id++;
    $('#' + id).append(GetStr(tr_id));
}
//新增试卷_删除行 
function deltr(id) {
    tr_id = $("#tQuestion>tbody>tr:last").attr("id");
    if (tr_id != 1) {
        $('#' + tr_id).remove();
    }
}
//动态添加一行 
function GetStr(tr_id) {
    var str = "<tr id='" + tr_id + "'><td><input type=\"text\" id=\"TxtTitle_"
            + tr_id
            + "\" name="
            + tr_id
            + " value=\"\"  style=\"width:90%\"/></td>";
    str += "<td><textarea style=\"width:90%; border: 1px solid rgb(164, 194, 204);\" id=\"TxtPrompt_"
            + tr_id
            + "\" cols=\"20\" rows=\"2\" name="
            + tr_id
            + "></textarea></td>";
    str += "<td><input type=\"button\" class=\"normalBtn\" id=\"btnQuestionAdd\" value=\"新增\" name=\"btnQuestionAdd\" onclick=\"addtr('tQuestion')\">";
    str += " <input type=\"button\" class=\"normalBtn\" id=\"btnQuestionDel\" value=\"删除\" name=\"btnQuestionDel\" onclick=\"deltr('tQuestion')\"></td>";
    str += "</tr>";
    return str;
}

$(function() {
    $('#tQuestion').append(GetStr(1));
})


<div>
<table cellspacing="0" id="tQuestion" border="1" rules="all" class="mainTab" style="width: 100%"> 
 <tr> 
    <th> 
        大题名称 
 </th> 
     <th> 
         大题说明 
  </th> 
      <th> 
         操作 
  </th> 
 </tr> 

</div>