Nested dropdowns?

I'm trying to create multiple nested dropdowns for use in an attribute agreement analysis, but cannot seem to get this to work beyond the 2nd column. I have a source sheet (Sheet2) that has 5 columns of data - each connected to the next.

I need to be able to create 5 dropdowns in Sheet1 that populate left to right based on the prior selection. The idea is that I want people to evaluate the test cases in Sheet1, and get the right options populated in the dropdowns from Sheet2.

I imported the workbook using the Zoho migration utility, but how do I nest the fields on the form so they maintain the correct relationship, and only show uniques?

Note: This is something I'm trying to port from an Excel 2007 workbook.

Many thanks in advance!!