Scenario is as follows:

I have 2 columns of which a data validation command is applied so that each
column only displays the selected drop down opions which the user may choose,
however, i need now to do the following:

If in column 1, an option is selected, column 2 must only present the sub
category options that apply to the option selected in column 1 & not all
options.

Any idea of this is possible in MS Excel 2003, if so, how would you do this?
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N.B.