after还是inMr.Whitewillcomeback(in)threedays.为什么正确答案是in?

Question

after 还是 in
Mr.White will come back (in) three days.为什么正确答案是 in?

Answer 1

将来时里,表示一段时间之后只能用介词in.
三天后我要去上海
I will go to Shanghai in 3 days （正确)
I will go to Shanghai 3 days later (错误）
我打算3年后结婚.
I plan to get married three years later.(一般现在时）
I'm going to get married in three years.（一般将来时）
Three days later he got to Beijing．＝After three days he got to Beijing．
他三天以后到达了北京.
这两个句子都是对的,一般过去时态两个都可以用.
请采纳答案,支持我一下.