I am trying to create a drop-down select menu that will consist of three select boxes, where the 3rd box will show/hide specific option based on an option selected in the 1s
There are several ways you can achieve that. From your example i can see that you only require 2 out of the 3 dropdown options to be filtering. Is this correct?
Please have a look HERE as it will cover many more scenarios that just the one you are mentioning.
An example with 3 dropdown options that filter each other: EXAMPLE
Hope this helps