U1E3 "y" , "..ir" preterites, and saber/conocer in preterite Practice this activity SEVERAL times because it will be different each time! WATCH! There are a few "..ar" and "..er" stem changers included. Remember that they do not stem change in the preterite. Watch for the special preterite meanings for SABER and Conocer. Tools This activity was created by a Quia Web subscriber. To learn how to make your own, just like this, click here.