They used a system of measurement called the Body Mass Index to define words like obese and overweight.

VOA: special.2009.07.21

The cells of this cluster inside next to the fluid filled cavity is a region of the blastocyst called the inner cell mass.

而这簇细胞的内侧,毗邻于充满液体的空腔的一侧,这些细胞在囊胚中称为内群细胞

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And this is called the atomic mass.

这是原子质量。

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We know there is no thing called a massless rope, but most ropes have a mass, but maybe negligible compared to the two blocks you are pulling, so we'll take the idealized limit where the mass of the rope is 0.

我们都知道无质量的绳子是不存在的,是绳子就有质量,但是相比于这两个物体就可以忽略不计了,所以我们有了这个理想的条件,即绳子的质量都是 0

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