Is it possible to do the following:

Column A is entitled "Crops" and offers a drop down box from which the user
will select one of three crops (ie. Broccoli, Savoy, Dutch White Cabbage).

Column B is entitled "Varieities".

If Broccoli has been selected in column A, I would like column B to offer a
drop down box listing all the varieties of Broccoli; but if Savoy has been
selected in column A, then I a drop down box to display all the varieties of
Savoy and likewise for Dutch White Cabbage.

Can this be done and if so how?

Help much appreciated.
Thanks