We're going to be left behind by the rest of the world.

我们就要落后于世界的其他地区了。

Every student studied hard in order not to be left behind by other students.

为了不落后于其他同学，每个学生都努力学习。

Everyone finds it necessary to update his knowledge, otherwise he will be left behind the society.

每个人都认为有必要更新自己的知识，否则将被社会抛在后面。

Why should Europe be left behind?

欧洲人为什么要落后呢？

You'll need to keep up or be left behind.

你需要跟上，或者被抛在后面。