说明：  参考有关资料，编了这个三级联动下拉表单的源代码，二级和四级联动下拉表单可以在此基础上简单改一下就行了。这个代码由于使用“-”作为分隔符，所以数据库中不能有“-”，如果一定要有“-”，可以把源代码改一下就行了。
(refer to the relevant information, provision of this linkage three drop-down form of source code, two and four drop-down interaction can form the basis of a simple change it there. Use the code "-" as the separator, the database can be "-" If there must be "-", the source code can change it there.)