谁帮我实现这个功能，高分。

我有一个表单，要实现select1改变，select2的选项也改变。我把变量放在了四个数组中：
maintype=arrar(0=>"","a","b","c");
sub1=array(0=>"","a1","a2","a3");
sub2=array(0=>"","b1","b2","b3");
sub3=array(0=>"","c1","c2","c3");
现在通过循环把maintype的值给select1,当select1改变为a,b,c时，怎样将select2分别显示sub1,sub2,sub3的值呢?
前提:只能在本页，不能提交到其他页，代码用php,或者js.我是个新手，最好加注释。
分不够，开新贴再加。
---------------------------------------------------------------

 1<form method="post" name="f1">
 2<?PHP   
 3$email="[email protected]";   
 4if(ereg("^[a-zA-Z0-9]+@[a-zA-Z0-9]+(\\.[a-zA-Z0-9]+)+$",$email))   
 5echo $email."正确<br>";   
 6else   
 7echo $email."不正确<br/>";   
 8  
 9$maintype=array(0=&gt;"","a","b","c");   
10$sub1=array(0=&gt;"","a1","a2","a3");   
11$sub2=array(0=&gt;"","b1","b2","b3");   
12$sub3=array(0=&gt;"","c1","c2","c3");   
13  
14echo '<select name="s1" onchange="submit()">';   
15for($i=0;$i<count($maintype);$i++) '<option="" echo="" if($_post[s1]="$maintype[$i])" selected="" value="'.$maintype[$i].'" {="">'.$maintype[$i];   
16else   
17echo '<option value="'.$maintype[$i].'">'.$maintype[$i];   
18}   
19echo '</option></count($maintype);$i++)></select>';   
20  
21echo '<select name="s2">';   
22if($_POST[s1]=='a')   
23$arr=$sub1;   
24else if($_POST[s1]=='b')   
25$arr=$sub2;   
26else if($_POST[s1]=='c')   
27$arr=$sub3;   
28else   
29$arr=array();   
30  
31for($i=0;$i<count($arr);$i++) '<option="" echo="" value="'.$arr[$i].'" {="">'.$arr[$i];   
32}   
33echo '</count($arr);$i++)></select>';   
34?&gt;   
35</form>

---------------------------------------------------------------

http://www.csdn.net/expert/topic/974/974562.xml?temp=.5239221
这是一个跟你相同的问题你去看看．ok?
---------------------------------------------------------------

http://www.csdn.net/expert/Topicview1.asp?id=723099
数据结构有所不同，所以修改如下

"","a","b","c"); $sub1=array(0=>"","a1","a2","a3"); $sub2=array(0=>"","b1","b2","b3"); $sub3=array(0=>"","c1","c2","c3"); ?> ``` ``` ``` ``` ``` ``` ```

1\---------------------------------------------------------------   
2  
3我给你讲一下思路吧：   
4采用将select中的值与select1中值进行组合,如:tt&amp;kk其中&amp;为分隔符!   
5当选中select中的值时，就从上面那个字符串提取第一个为tt的字符，并将其进行分解，存入select1中就可以