fall back on sth

fall back on sth的意思是借助于；依赖，依靠，和live by差不多，形容靠…谋生。

As men do not live by bread alone, they do not fight by arms alone.

如同人们并不单靠着面包生活，他们也不单靠着武器来作战。

play up to sb

play up to sb有“讨好，巴结”的意思，也表示“给…当配角”。

Julia knows how to play up to the supervisors - she can always get time off work when she wants it.

朱莉娅懂得如何讨好上司——这样她随时都能请假。