In all existing life forms, the four "letters" of the genetic code, called nucleotides, are read in triplets, so that every three nucleotides encode a single amino acid.

在所有现有的生命形式中的四个“字母”的遗传密码，即核苷酸，是以三个为单位读取的，每三个核苷酸编码成为一个单独的氨基酸。

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The four existing service providers will deliver service in different time periods, and at different costs.

现有的四个服务提供商交付服务的时间和成本不同。

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Figure 1 shows the four pieces of m17n and how the libraries correspond to existing system components.

图1给出了m17n的4个部分，以及这些库是如何与现有的系统组件对应的。

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The home secretary argues the existing four Welsh forces are too small to deal with the demands of modern policing.

BBC: NEWS | UK | Wales | MPs criticise police merger plans

In the world of Oz memorabilia, Shaw is best known for having owned one of the four existing pairs of Dorothy's ruby slippers.

FORBES: Swept Up

So Ed Richards is pleased that along with the four existing operators - Vodafone, O2, EE and Three - the winners include a new player, Niche.

BBC: 4G: The results are in