How do I set up a list box say B that will depend ont eh answer of A?

I want to create a listbox so that A will be a choice of the school district
the student attends and Listbox B will be a choice of the schools within that
district.

I do not want to create the listbox B to be a choise of 67 schools from all
districts in our area. Thanks for the help!
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Thanks,,
Kim