有人知道怎么把下面这段代码改成按回复时间来排序吗？
{eval $pid=$category['pid'];}
<div class="container collection index" style="padding-top:20px;">
<div class="row" style="padding-top:0px;margin:0px">
<div class=" col-md-17 main bb" style="padding-top:10px;margin-top:0px;">
<div class="row">
<div class="col-md-24">
<div class="row">
<div class="">
<div class="" style="padding:15px;margin:15px;">
<div>
<div class="course-filters">
<div class="row filters-wrapper filter-categorys-wrapper no-margin">
<div class="filter-title-wrapper col-sm-24 col-md-4">
<span class="filter-title" >
一级：
</span>
</div>
<div class="filter-item-wrapper col-md-20">
<a href="{eval echo str_replace('.html','',url('ask/index'));}">
<span class="filter-item {if $cid=='all'||!$cid}active{/if}">
全部
</span>
</a>
{eval $catlist=$this->getlistbysql("select id,name,displayorder,grade from ".$this->db->dbprefix."category where iscourse=0 and isuseask=1 and grade=1 and pid=0 order by displayorder asc limit 0,100");}
{if $catlist}
<!--{loop $catlist $index $cat}-->
{if $index<15}
<a href="{eval echo getcaturl($cat['id'],'ask/index/#id#');}">
{if isset($pid)&&$pid!=0}
<span class="filter-item {if $pid==$cat['id']}active{/if}">
{else}
<span class="filter-item {if $cid==$cat['id']}active{/if}">
{/if}
{$cat['name']}
</span></a>
{/if}
<!--{/loop}-->
<!--{loop $catlist $index $cat}-->
{if $index>=20}
<a class="morecat" href="{eval echo getcaturl($cat['id'],'ask/index/#id#');}">
{if isset($pid)&&$pid!=0}
<span class="filter-item {if $pid==$cat['id']}active{/if}">
{else}
<span class="filter-item {if $cid==$cat['id']}active{/if}">
{/if}
{$cat['name']}
</span></a>
{/if}
<!--{/loop}-->
{if count($catlist)>=20}
<div class="more_link showmore" style="width:90%;">
<a rel="nofollow">查看更多</a>
</div>
{/if}
{/if}
</div>
</div>
{if isset($pid)&&$pid!=0}
{eval $_cid1=intval($pid); $subcatlist=$this->getlistbysql("select id,name,displayorder,grade from ".$this->db->dbprefix."category where iscourse=0 and isuseask=1 and grade=2 and pid=$_cid1 order by displayorder asc ");}
{else}
{if isset($cid)&&$cid!='all'}
{eval $_cid1=intval($this->category[$cid]['pid'])!=0 ? intval($this->category[$cid]['pid']):$cid; $subcatlist=$this->getlistbysql("select id,name,displayorder,grade from ".$this->db->dbprefix."category where iscourse=0 and isuseask=1 and grade=2 and pid=$_cid1 order by displayorder asc ");}
{else}
{eval $subcatlist=$this->getlistbysql("select id,name,displayorder,grade from ".$this->db->dbprefix."category where iscourse=0 and isuseask=1 and grade=2 order by displayorder asc ");}
{/if}
{/if}
<div {if $cid=='all'||count($subcatlist)==0}style="display:none;"{/if} class="row filters-wrapper filter-categorys-wrapper no-margin">
<div class="filter-title-wrapper col-sm-24 col-md-4">
<span class="filter-title" >
二级：
</span>
</div>
<div class="filter-item-wrapper col-md-20">
{if $pid==0}
<a href="{eval echo getcaturl($cid,'ask/index/#id#');}" rel="nofollow">
{else}
<a href="{eval echo getcaturl($pid,'ask/index/#id#');}" rel="nofollow">
{/if}
<span class="filter-item {if $cid=='all'||!$cid||$pid==0}active{/if}">
全部
</span>
</a>
{if $subcatlist}
<!--{loop $subcatlist $sindex $subcat}-->
{if $sindex<20}
<a href="{eval echo getcaturl($subcat['id'],'ask/index/#id#');}"> <span class="filter-item {if $cid==$subcat['id']}active{/if}">
{$subcat['name']}
</span></a>
{/if}
<!--{/loop}-->
<!--{loop $subcatlist $sindex $subcat}-->
{if $sindex>=20}
<a class="moresubcat" href="{eval echo getcaturl($subcat['id'],'ask/index/#id#');}"> <span class="filter-item {if $cid==$subcat['id']}active{/if}">
{$subcat['name']}
</span></a>
{/if}
<!--{/loop}-->
{if count($subcatlist)>=20}
<div class="more_link showmoresub" style="width:90%;">
<a rel="nofollow">查看更多</a>
</div>
{/if}
{/if}
</div>
</div>
</div>
</div>
<hr>
</div>
</div>
</div>
</div>
</div>
