?????? ???? ???????????? ?????? ????????????.The 2 most popular grammatical principles where by this happens is when conjugating in the past or current tenses. For examples:?? ???? ??????, ????????????, ???? ???? (???????? ??)????, ?????? ?????? ?? ??? ?????????? ????(?? ?????????? ?? ????????????- ????????? ?? ???????????? ???? ????????? ????.?? ?