Practically all of the heat energy received by the earth comes from the sun.

现在我们对原子内部的情况已相当清楚了。

地球所得到的热能几乎都来自于太阳。

在这一章中，我们的任务是弄清空气的构成成分。

4.2 人称代词的译法

第2节 翻译练习1

You can decide what resolution and compression level is best for your output.

We’ll do everything possible to improve the supply of electricity.

You can find the density of a body providing you know its mass and volume.

We must be very careful to avoid trying to express energy in terms of power units.

我们将尽一切努力来改善电力供应。

只要知道物体的质量和体积，就可求出物体的密度。

你可以决定哪种溶解和压缩程度对成品最好。

必须注意避免用功率单位表示能量。

第2节 翻译练习2

It may require the taking of a large sample as in macro analysis.

If an atom contains three protons, it must have three electrons to be electrically neutral.

如果一个原子有三个质子，这个原子必然有三个电子来使其呈电中性。

它可能要求像宏观分析中那样采用大的样本。

4.3 形容词性物主代词的译法

第3节 翻译练习1

The density of anything is its mass per unit volume.

Each substance shows an individual structure of its own.

One of the drawbacks of the early lasers was their inability to operate continuously.

每一种物质都显示出它自己的独特结构。

任何物体的密度是它的每单位体积的质量。

早期激光器的缺点之一是它们不能连续地工作。

第3节 翻译练习2

In their workshop there is no one who understands how a computer uses its tubes.

Transistors are more advantageous to vacuum tubes for their being small and light.

The transformer cannot be called a machine because of its having no moving parts.

晶体管优于真空管，因为它尺寸小、重量轻。

在他们车间，无人能理解计算机是怎样使用其电子管的。

变压器不能称为机器，因为它没有转动的部件。

第3节 翻译练习3

According to their ability to conduct electric current, all materials may be classified into three major categories: conductors, semiconductors and insulators.

You shouldn’t have touched the wire with your wet hands.

你不该用湿手触摸导线。

根据导电的性能不同，所有的材料可分为三大类：导体、半导体和绝缘体。

第3节 翻译练习4

Heating semiconductors means increasing their conductivity.

Triangles can be classified according to their angles or the relative lengths of their sides. According to their composition, these raw materials may be separated into three groups.