Prevent duplicate survey ranking response

[jkitterm]

I am creating a survey in Excel 2013 and asking participants to rank 5 items. I want to create a drop down box next to each item with the choices of

1
2
3
4
5
NA

but limit what they can select if they have already ranked another item in the list. Essentially trying to prevent them from being able to rank two items with the same number. Also, they can give multiple items a NA ranking.
NOTE: I am not proficient in VB so please for any solutions do not suggest VB Code.

Thanks