平流层大气包含臭氧层，臭氧层由紫外线照射导致的三个氧原子结合成的臭氧分子组成。
The still air of the stratosphere contains the ozone layer, which was created when ultraviolet light caused trios of oxygen atoms to bind together into ozone molecules.
外因遗传是一种可以传给下一代细胞的基因调控过程，最常见的方式是通过甲基化作用来完成，该作用可以让甲基（由一个碳原子和三个氢原子组成）附着于腺嘌呤或胞嘧啶上。
Epigenetics is a type of gene regulation that can be passed from a cell to its daughters. The most common mechanism is methylation.
锂原子是由三个电子、三个质子和四个中子组成的。
The atom of lithium is made up of three electrons, three protons and four neutrons.
锂原子是由三个电子、三个质子和四个中子组成的。
The atom of lithium is made up of three electrons, three protons and four neutrons.
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