jquery设置单选框、复选框、下拉框的选中状态

<select id="single">   
  <option value="1">下拉选项1</option>   
  <option value="2">下拉选项2</option>   
</select>   
<br><br>

<select id="multiple" multiple="multiple">   
  <option value="1">下拉选项1</option>   
  <option value="2">下拉选项2</option>   
  <option value="3">下拉选项3</option>   
</select>   
<br><br>
<input type="checkbox" name="c" value="1"/> 复选项1    
<input type="checkbox" name="c" value="2"/> 复选项2    
<br><br>
<input type="radio" name="r" value="1"/> 单选项1    
<input type="radio" name="r" value="2"/> 单选项2  
<br><br>

<script type="text/javascript" src="http://www.aspbc.com/js/jquery.js"></script>
<script type="text/javascript">
$("#single").val(2);    
$("#multiple").val([2, 3]);    
$("input[name='c']").val([2]);    
$("input[name='r']").val([2]); 
</script>