Because it takes three units where there's only four choices at each position to have at least 20 unique combinations.

因为每个位点上仅有四种可能性,只有采用三个碱基一组,才能取得至少二十种不同的组合方式

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There are 64 combinations of three bases and I only need to describe 20, so there's combinations to spare.

三个一组的碱基产生六十四种组合,而我只需对应二十种氨基酸,所以一种氨基酸会对应不同密码子

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In the meantime, what Saussure is doing with this relationship above and below the line is, he is saying that there is an arbitrary relationship between the concept and the sound image.

同时，索绪尔觉得这组关系,也就是线上和线下的这个组合，他说，这是一个任意的组合,在事物和声音形象之间。

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I'd only have 16 possible two base sequences, that's not enough to specify over 20 amino acids.

如果两个碱基一组那一共只有十六种组合,不够和二十种氨基酸来一一对应

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If I have three, I have 16 x 4 or 64 possible choices, way more than enough.

那如果是三个碱基一组,那就有16x4种,六十四种组合,那就足够了

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