he doesn't know beans about insurance business at all.
他对保险业务一窍不通。
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名词bean,本意是“豆子”。在俚语中,引申为“很小的量”(A small amount)。因此,not know beans about sth.,作为一个固定搭配,就表示,对某事一窍不通,不了解。
例句:
I don't know beans about investing. 我一点也不懂投资理财。