??????? ???? ?????? ?????? ?????? ??????? ??????? ?????? ??????? ?? ?????: ????? ???????? ??????????.?????? ????? ???? ???? ??? ?????? ?????? ??? ???? ?????? ??? ???? ???? ??????? ?? ???? ?????? ???????? ??? ????? ??? ?????? ?? ??????? ?????? ?????? ?? ????? ???????? ???????? ???????.I've study some enterprise textbooks and I feel This is often cer