Conditional Dropdowns that pull .CSV file

I'm very new javascript, and what I'm trying to do is create a program where I ask a question and dropdown box about which location they are in, and there are 6 options. Then based on their location there is another dropdown box that is pulling data from a particular .CSV file on my hard drive. And once they choose from that dropdown I have a Powershell script that will take the info from both dropdowns and run.

I've gotten the first dropdown completed, but I'm struggling to figure out how to add the second dropdown and what order the code should go.

This is what I have for the second part:

<script>if (!event.DCdropdown("Dallas") {

src="C:\xxxx"}

Any help or pointing me in the right direction is much appreciated.