MVC下拉列表级联 - 当第一个ddl选择发生变化时，如何在第三个ddl上触发事件？

I have three DDL's in a view. I fire a javascript function on 'onchange' of the first DDL to populate the second, and of the second to populate the third. Works fine.I have three DDL's in a view. I fire a javascri