bread and butter

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释义
主要收入来源，生活来源；生计，谋生之道
That which is central or fundamental, as to one's business, survival, or income; a staple or cornerstone.

例句
Raj: I'm a scientist. My ability to think is my bread and butter. (The Big Bang Theory)
拉什：我是科学家。我的技能就是生活来源。（生活大爆炸）