1. it is up to somebody: if you say it's up to someone, you mean that that person should make the decision about something, and no one else

备注：一般用在口语中。

例：

"Where would you like to go this evening?" "It's up to you - it's your birthday."

（-你今晚想去哪？ -你定吧，今天是你生日。）

it is up to somebody what/when/whether etc.

It's up to them what they do with their money.（ 他们的钱要怎么花，全凭他们。）

it is entirely up to somebody

I think you should take the job, but of course it's entirely up to you. （我觉得你该接受这份工作，当然，还是全凭你自己做主。）

2. be for somebody to decide: use this when only one person or group has the right or authority to make a decision about something important

备注：这是较正式的说法。

例：

We cannot say if he's guilty or not. That is for the court to decide. （我们没法说他有罪还是无罪，这要由法庭裁定。）

it is for somebody to decide what/whether/when etc.

It's for you to decide whether you go to university or not - not your parents. （该由你自己来决定你要不要上大学，而不是由你父母来决定。）

3. the ball is in your court: if the ball is in your court , it is your turn to make a decision or do something

例：

I've told you what I think of your idea—the ball's in your court now. （我已经说了对你的想法的看法，这下该你自己做决定了。）

What do you think we should do now? The ball is in your court. （你觉得我们现在该怎么办？轮到你做决定到了。）

The terrorists had made their demands clear and the ball was in the government's court. （恐怖分子已经把要求说得很清楚了，现在该政府做决定采取行动了。）

再看《老友记》S05E07的例子：

情境：Rachel对邻居Danny有好感，但Danny没有主动约她出去，Rachel以为Danny欲擒故纵。所以当Danny想请Rachel她们去参加派对时，Rachel假装很忙拒绝了。看看她心里是怎么盘算的吧。

Monica: You wanted him to invite you to the party and he did it!

Rachel: Yeah, but he waited until the last minute! So if I said yes, he would know I had nothing better to do than wait around for an invitation to his stupid party. I said, "No!" which puts me right back in the driver's seat.

Monica: Great. So the ball is in his court?

Rachel: Ball? There is no ball.

大意：

Monica: 你不是就想他请你去派对吗？他也请啦，你还想怎么样？

Rachel: 但他最后一刻才请我，假如我答应，他就知道我除了等他的邀请之外，再无事可做。但我拒绝了，这让我再占上风。

Monica: 哦，这下该他出招了。

Rachel: 招？他没招了。

4. rest with: if a decision rests with someone, they have the authority to decide what should be done

例：

The final decision rests with you. （该由你来做最终决定。）

The committee has made certain recommendations, but the final decision rests with the President.（委员们提了一些建议，但最后决定权在总统。）

Responsibility for any military operation always rested with the commander. （军事行动向来由指挥官全权负责。）