这些政策变更正在经济不确定的背景下发生。

These policy changes are taking place against a ___background of economic uncertainty.

你能提供一些关于这个项目如何启动的背景信息吗？

Could you provide some ___background on how this project started?

要理解角色的行为，你需要了解这部小说的历史背景。

To understand the character's actions, you need to know the historical ___background of the novel.