Userform Listbox data from different workbooks

Please help, I have created an userform listbox in workbook A and RowSource points to a specific range of values in a particular sheet in workbook A. The macro is activated by CTL(z). This part works fine as long as the active workbook is A. I want to activate the listbox from a different active workbook say B. The List box appears but no data because the rowsource points to a range in workbook A. I have tried to put Workbooks("workbook A") in rowsource but still no success. Any suggestions would be appreciated.

Your rowsource would look like:

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for example. As an aside though, I think it's better not to use the rowsource and to load the data in code.