Mary, this is Stone's brother Jim.

玛丽，这是世通的兄弟吉姆。

You've been a great help.

你帮了大忙。

She complained, with reason, that she had been underpaid.

她抱怨她的工资一直很低，这也不无道理。

He's busy preparing for class.

他忙着准备功课。

He's gone for the day.

他整天都不在。

I'm sorry, I really don't know.

对不起，我真的不知道。