## R, versions 2 and 3, 16 bytes

    exists("cite")+2

This command returns `2` for R 2.x.x and `3` for R 3.x.x. The function `cite` was added in R version 3.0.0. Therefore, the command `exists("cite")` returns `FALSE` for R 2.x.x and `TRUE` for R 3.x.x.

## R, all versions (1, 2, and 3), 33 bytes

    exists("cite")+exists("eapply")+1

The function `eapply` was introduced in R 2.0.0.