It may be a little more complex than that - in the condition builder for the filter on drop down b, you'd select the abbreviation from B. Then is equal to and in the third dropdown, use a formula. In the formula, you'd pick the abbreviation from data source A and add a filter - in that filter, you'd select the region in data source A is equal to the selected region in the form. Hope that makes sense. :)
Hilary Stoupa
