这本书是他在早期文章中提出的想法的延伸。

The book is an ___extension of ideas he set out in an earlier article.

所以我们可以说电脑是我们大脑的延伸。

So we might say the computer is the ___extension of our brain.

这个移动应用是公司在线服务的延伸。

The mobile app is an ___extension of the company's online services.