他在这个诊所里当了三年医生了.
he has _worked___ _as____ __a____ ___doctor__in the clinic for three years.
我不知道他是否故意把这本书落在这里.
i don't know _if___ he __drops____the book here __on ___ _purpose____.
到会议结束时,他还没有露面.
____Untill__the time the meeting was ___over___,he hadn't __shown ___ ____up__.