Restricting data entry to 1 of 3 cells

[Gunnjg]

I have an excell sheet with 3 columns. Each column has a drop down list. Once a choice is made in a column I need the other two columns to not have data.
It is a rating. Column 1 holds ratings of 1, Column 2 holds ratings of 2, Column 3 holds rating of 3. Only one choice can be made 1,2 or 3. So if a user choses Column 1 and then decides to increase the rating, when he enters the 2 or 3 the original answer in 1 is removed.

I know it could be handled with a single column with data validation restricting the answer to 1,2,or 3. But the person I am doing this for wants three coulmns.