I am having trouble trying to figure this one out:

I am having customers fill out a form for me in excel, and am running into
issues with the data they are inputting. I think the best way to correct this
would be to restrict the fields that they can edit.
For instance: If a customer chose 'BI' from the drop down menu in column A,
I want him/her to be able to edit the neighboring cell in column B. Either by
having Column B hidden naturally, and only shown when 'BI' is selected, or
have it shown but can only be edited when 'BI' is selected.