1. Navigate to Contacts > Database Management > Field Management > Manage Custom Fields
  2. Click Add Field by Custom Profile Fields
  3. Give it a name
  4. Select Dynamic Dropdown
  5. In the "Enter Options" box, put in each option you wish to appear in the dropdown, then click "Add" after each
  6. When you have entered all of the options, click Save and Add Level
  7. This will refresh the screen, and now you can add the options to appear in the new dropdown box that will appear, when each of the options from step 5 have been selected.