Query to check form selection

[ben h]

I don't know how best to describe this, except with an example of what i
want to do:

A table holds choices made by a user in response to a series of
questions, but for each question in the response (a response equates to
a record) there is a rule that if she chooses a, or b for any question
in that response, then she can't choose anything else for that response.

So, for response 1, there are 6 questions each having 5 options. From
the 5 options, she can choose from a,b,c,d, and e. She can select
multiple options, unless she chooses a or b, in which case that's all
she can choose.

Basically you can imagine it by thinking of a form, showing multiple
rows/records. For each record, there are 6 combo boxes with the 5
choices. The user may choose anything she likes, unless in any of the
cbs she chooses a or b, in this case that is all she shall be allowed to
select for that record, the rest must remain empty.

The tables look like this:

Responses
id (PK)
Q1 (FK=Choices.id)
Q2 (FK=Choices.id)
Q3 (FK=Choices.id)
Q4 (FK=Choices.id)
Q5 (FK=Choices.id)
Q6 (FK=Choices.id)

Choices
id (PK)
choice (text)


I'm using the BeforeUpdate event of the Form to trigger the test, and
have tried using a SQL query but I'm not having much luck, would anyone
have a suggestion?!

Thanks in advance!
Ben