1.in：过……后（未来时间）注意如果用于过去时，用after +时间。She went to Nanjing last May，and she came back after a month.去年五月她去了南京，一个月之后她又回来了。大多用在将来时（一般将来时和过去将来时）。in an hour 一小时之后in a week or so 一个多星期之后He will be back in five hours.他五小时之后回来。They said they would arrive here in a week.他们说他们一周后到达。2.within：不超过……的范围比较within和in with in强调在……时间之内，没有时态的限制。in是以现在为基准，in an hour是指从现在起1小时之后，所以一般只用于将来时。within 3 hours 3小时之内I must finish painting the cat within five minutes.我必须在五分钟之内画好这只猫。They worked hard. They finished the workwithin 2 days at last.他们努力工作，结果终于他们在两天之内完成了这项工作。