List box B IF list BOx A equals
 

I am trying to create listboxes that Listbox A will contain a choice of
school districts and listbox B will be the schools in that particular
district. However I do not want to include all 60 plus schools in "B"
therefore I want to make listox B inclusive of the district of the choice
that was input for A. (I hope this makes sense)

How do I set up the listbox for B and the ranges depending on the response
of A? I am assuming that it to be an IF statement ..........
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Thanks,,
Kim