1.After作介词 prep. ，后面可以加做宾语的动名词（V+ ing），名词，代词，翻译成 “时间上或者空间上在...之后”
如：He came back after 5 o'clock 他五点以后返回来了。
He ran after the bus. 他在那辆公交车后追着跑。
I went to bed after having finished my homework 我完成作业后睡觉了
I will go to bed after drinking the milk. 我喝完牛奶后要睡觉
2.After 也可以当连词 conj.，用来连接2个句子
I went to bed after I have finished my homework 我完成作业后睡觉了
3. After 和 in 的区别
意思都是“一段时间以后”
"一般 " After用在过去时，in用在将来时
He will come back after 5 o'clock (X 错误)
He will come back in 5 o'clock (V 正确)
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一句多译： Jack 经常放松 15 分钟然后做作业。
Jack usually does homework after he relaxes for 15 minutes
Jack usually does homework after relaxing for 15 minutes.
Jack usually relaxes for 15 minutes and then he does his homework.