Ajax向同一页面发送空值

I've got a form on my page:

我的页面上有一个表单:

<form id="extended-search" >
<div class="input-container">
<select class="select" name="sex" id="sex">
<option value="0">All</option>
<option value="1">M</option>
<option value="2">F</option>
</select>
</div>
<input type = "button" class="searchButton" value = "Show" onClick="submitSearch();">
<img id="loading" src="img/ajax-loader.gif" alt="working.." />
</form>
<fo