He will come back in an hour.对in an hour 提问

He will come back in an hour.对in an hour 提问

He will come back (in an hour)提问
how soon will he come back?
how long 多长时间 回答是for+一段时间
欢迎追问

how long 多长时间

When will he come back.

When will he come back？

用how sonn提问（多久）
in an hour 这里表示一小时之后（表示将来）