I think by five o'clock the children (C.will have return) from their work.我認(rèn)為到五點鐘之前,孩子們都已經(jīng)下班回家了.時間狀語by five,意為“截止到五點時（已經(jīng)做了）”,它用于完成時態(tài).而賓語從句的動作是還...哦，那像這種呢：i（）there five minutes when all the lights ().A.had been/went. B.have been/go選擇A。從句過去時，主句是過去完成時。