Jon Alterman says King Abdullah is striking a delicate balance between the two powers - because China needs Saudi oil and the Saudis need U.S.security to keep the oil flowing worldwide.

VOA: standard.2010.06.29

It's because there's a balance between the two.

这是因为这两个两之间有一个平衡。

麻省理工公开课 - 热力学与动力学课程节选

Isn't it difficult being a mother and a professor at the same time and keeping a balance between the two?

同时做母亲和教授是不是很困难呢？两者之间取得平衡不容易吧？

教授的梦想 - SpeakingMax英语口语达人