真菌在腐化过程中十分重要，而腐化过程将化学物质回馈于土壤，提高其肥力，并分解动物粪便。
19. When it is struck, a tuning fork produces an almost pure tone, retaining its pitch over a long period of time.
音叉被敲击时，产生几乎纯质的音调，其音量经久不衰。
20. Although pecans are most plentiful in the southeastern part of the United States, they are found as far north as Ohio and Illinois.
虽然美洲山河桃树最集中于美国的东南部但是在北至俄亥俄州及伊利诺州也能看见它们。
21. Eliminating problems by transferring the blame to others is often called scape-goating.
用怪罪别人的办法来解决问题通常被称为寻找替罪羊。
22. The chief foods eaten in any country depend largely on what grows best in its climate and soil.
一个国家的主要食物是什么，大体取决于什么作物在其天气和土壤条件下生长得最好。
23. Over a very large number of trials, the probability of an event’s occurring is equal to the probability that it will not occur.
在大量的实验中，某一事件发生的几率等于它不发生的几率。
24. Most substance contract when they freeze so that the density of a substance's solid is higher than the density of its liquid.
大多数物质遇冷收缩，所以他们的密度在固态时高于液态。
25. The mechanism by which brain cells store memories is not clearly understood.
大脑细胞储存记忆的机理并不为人明白。
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