1. beat the air

释义：To keep doing something despite its apparent pointlessness or futility. （尽管没有意义，是徒劳还是不停地做某事，白费劲地做事）

例句：There's no way he'll get his progressive agenda through—he's just beating the air.

他的进步议程是不可能通过的——他只是白费力气。

Tom is so infirm of purpose and you beat the air by going to ask him for advice.

汤姆这人优柔寡断，向他征求意见是徒劳无益的。

You're beating the air by asking him to lend you money.

你向他借钱是白费力气。

2. hot air

释义：Lies, exaggerated talk , or nonsense. （胡说，谎言，吹牛）

例句：Oh, you can't believe a word that guy says—he's full of hot air.

噢，那家伙说的话你一个字也不能相信——他满口空话。

That station broadcasts nothing but a bunch of hot air.

那电台播放的是一堆谎言。

That man at the party yesterday didn't have any idea what he was talking about. He blew a lot of hot air about health and nutrition. He didn't know that both of us have been practicing medicine for more than thirty years.

昨天聚会上那个人真不知道他在说什么。他夸夸其谈地说了好多关于健康和营养的事。他可不知道我们两行医已经三十多年了。

Most candidates make promises during a campaign to win voters' support. But many promises are nothing but hot air. After the candidates get elected, they tend to forget most of the things they promised to achieve.

大多数候选人在竞选过程中都做出各种保证以赢得选民的支持。但是，他们说的好多都是谎言。等到当选后，他们往往把自己的保证忘了。

3. into thin air

释义：Completely gone or disappeared. （完全消失，无影无踪）

用法：它是介词短语，和动词diappear，vanish连用作谓语。

例句：I have no idea where my keys have gone. They seem to have disappeared into thin air!

我不知道我的钥匙哪儿去了，它们好像凭空消失了!

I couldn't find her anywhere, she seems to vanish into thin air.

我到处找不到她，她好像是消失得无影无踪了。

The brutal dictatorship was so mercilessly efficient that anyone who stood up against it soon vanished into thin air.

这个残酷的独裁政权是如此的有效力，任何反抗它的人都很快消失得无影无踪。