be back的用法和樣例：
例句
- His parents demanded that he (should) be back by ten.
他的父母要求他十點以前回家。 - Could you give me a rough idea when you'll be back?
你能告訴我你大概什麼時候回來嗎？ - I won't be back till 11:00.
我11點以前回不來。 - I'll be back soon.
我馬上回來。 - She longed to be back in China.
她渴望回到中國。 - You must be back by four o'clock.
你務必在4點前回來。 - I'll be back in an instant.
我馬上就回來。 - It is expected that John will be back by ten.
約翰在十點以前回來是預料中的事。
