I'm wondering if this is possible with a data validated list. I'd rather not use VBA code if at all possible.

Column-A represents a data validated drop-down list of 3 values: a,b,c

Column-B to be a conditional data validated drop-down list (right now 3 values maybe a few more in the future). If Column-A = "a" can Column-B present a drop down list of 1,2,3? For any other value in Column-A Column-B yields a blank cell or NA.

Column A Column B
a (select 1,2,3)
b NA
b NA
b NA
a (select 1,2,3)
b NA
a (select 1,2,3)
c NA