jQuery新增标签之后添加监听

<table id="tb">
<tr id="row1">
<td>
部位：
</td>
<td>
<select class="buwei" style="width:150px">
<option value="">请选择</option>
</select>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</td>
<td>
指标：
</td>
<td>
<select class="zhibiao" style="width:150px">
<option value="">请选择</option>
</select>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</td>
<td>
<hr class="#2ab1d8" style='height:10px;width:120px; border:none;border-top:5px solid #66ccff;'/>
</td>
</tr>
</table>

$("#tb").on("change",".buwei", function(){

debugger;
var select = $(this);
var id=select.val();
$.ajax({
url:'../servlet/qstServlet?method=listChild',
type:'post',
async:'true',
data:{
id:id
},
dataType:'json',//返回的数据格式
success:function(data){
var json = JSON.stringify(data);
var zb = select.parent().parent().find(".zhibiao")[0];
zb.options.length=0;
for(var i = 0;i<data.length;i++){
zb.add(new Option(data[i].text,data[i].text),null);
}
console.log(data);
},
error:function(xhr,textStatus){
console.log('错误');
}
});
});