(一):Let's give him a big hand.

让我们热烈鼓掌欢迎他。

Let's give her a warm welcome!
让我们以热烈的掌声欢迎她!
Let's clap her on.
让咱们鼓掌欢迎她上来。

(二):We appreciate them for their contributions to the US-China relationship.

我们感谢他们为美中关系作出的贡献。

We would like to thank John for his tremendous contribution.
我们要感谢约翰作出的巨大贡献。
Finally, we do appreciate the contribution that everybody makes for the company.
最后，我们非常感谢大家为公司作出的贡献。