1.After作介詞 prep. ，后面可以加做賓語的動名詞（V+ ing），名詞，代詞，翻譯成 “時間上或者空間上在...之后”
如：He came back after 5 o'clock 他五點以后返回來了。
He ran after the bus. 他在那輛公交車后追着跑。
I went to bed after having finished my homework 我完成作業后睡覺了
I will go to bed after drinking the milk. 我喝完牛奶后要睡覺
2.After 也可以當連詞 conj.，用來連接2個句子
I went to bed after I have finished my homework 我完成作業后睡覺了
3. After 和 in 的區別
意思都是“一段時間以后”
"一般 " After用在過去時，in用在將來時
He will come back after 5 o'clock (X 錯誤)
He will come back in 5 o'clock (V 正確)
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一句多譯： Jack 經常放松 15 分鍾然后做作業。
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.