学生们在做实验前分成四组。

The students were into four groups before doing experiments.

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有时，所有的学生被老师分成四组进行讨论。

Sometimes, all of the students are divided into four groups by the teachers while having a discussion.

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他们被随机分为四组，并被置于不同等级的背景噪音环境中，从完全寂静到有50分贝、70分贝和85分贝的噪音。

They were randomly divided into four groups and exposed to various noise levels in the background, from total silence to 50 decibels, 70 decibels, and 85 decibels.

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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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I play through BioShock, and Left 4 Dead and Left 4 Dead 2,

我玩过“生化奇兵”、“生死四人组”和“生死四人组2”，

电子游戏 - SpeakingMax英语口语达人

It was regular and it happened to involve four chords.

这是规则的，一共四组和弦发生了规则的改变。

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