Select Validation Not Working

I have a form used for booking courses (on this page). However, the select boxes do not come up as a validation error when I leave them blank however and submit the form.

I am using “include_blank” in the form settings, and have set an id for the select so I can edit the blank field with jquery (using this code).

Can someone advise me on how to solve?

https://wordpress.org/plugins/contact-form-7/