下面这段该怎么修改才能实现设置默认值？
public function ajax_getcity(){
$proid= $_POST['proviceid'];
$citylist=db('district')->where(array('pid'=>$proid))->select();
$content = '';
for($i=0;$i<count($citylist);$i++) {
$content =$content."<option value='".$citylist[$i]['id']."' {if condition='".$citylist[$i]['id']." eq 410'}selected{/if}>".$citylist[$i]['title']."</option>";
}
$data = array(
'content'=>$content,
);
$provinces_json = json_encode($data);
exit($provinces_json);
}