这个新理论是他早期工作的延伸。

The new theory is an ___extension of his earlier work.

许多人认为智能手机是我们个人身份的延伸。

Many consider the smartphone an ___extension of our personal identity.

这部续集是电影原故事的自然延伸。

The sequel was a natural ___extension of the film's original story.