Hello, I am quite new in moodle and I really need the help of the geek from this forum. I would like to know how can I customize the registration field or user edit field with this situation. When I choose valve the first drop down list
and then I will able the choose the another value from drop drown list that depend on the first one. 
Second value content of drop down list is totally depend on the first user input valve. Is that possible with moodle from and if so, I am very glade if someone show how to do it. Thanks in advance.
Best Regards,
Han
Such a functionality is not part of the forms library that Moodle uses. In theory should be doable via a custom code.