从db中拉出的级联下拉框

I'm trying to make two dropdown boxes that are populated from a db using php and ajax. The first dropdown box only has one selection but when you select it, it should populate the second drop down box with different departments from my school being pulled from the database. On selecting a department all the courses from that department should be displayed in a third drop down box. Right now I'm just trying to get the dropdown box with all the departments to populate, it doesn't populate anything right now when you click it. I think there's a problem with the loop to write the names of the departments in the drop down box. Here's my codeI'm trying to make two dropdown boxes that are