他们对丛林中四只乌鸦进行了试验研究。这四只乌鸦都是日本城市经常看见的品种，由于繁殖过快，常常看作是城市祸害。

The study involved experiments conducted on four jungle crows, the type most commonly found in Japanese cities and often regarded as an urban nuisance due to their booming population.

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他们告诉路人这是四件不同的睡衣以及四双不同的袜子，并要求路人对睡衣和袜子作出评价。

Passersby were asked to evaluate what they were told were four different nightgowns and four different pairs of stockings. In fact, all four items were identical.

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其一是在过去四个月中，欧元对美元贬值了超过四分之一。

One is that the euro has plunged by over a quarter against the dollar in the past four months.

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For the carbon, we start with 4 valence electrons, we have 0 lone pair electrons minus 4, and we end up with a formal charge of 0.

对于碳，我们从四个价电子开始，我们有零个孤对电子，再减去四，最终我们有零个形式电荷。

麻省理工公开课 - 化学原理课程节选

It shows an assessment of reading proficiency levels in fourth grade.

这项研究对,四年级同学的阅读熟练程度。

麻省理工公开课 - 媒体、教育、市场课程节选

So, if we want to figure out the formal charge on the carbon, we need to take the number of valence electrons, so that's 4. We need to subtract the lone pair, what number is that? It's 2.

如果我们想算出碳原子的形式电荷，我们需要将价电子的个数，也就是四，减去孤对电子的个数，它是多少？是二。

麻省理工公开课 - 化学原理课程节选