21、Essentially, a theory is an abstract, symbolic representation of what is conceived to be reality.
理论在本质上是对认识了的现实的一种抽象和符号化的表达。
22、Thanks to modern irrigation, crops now grow abundantly in areas where once nothing but cacti and sagebrush could live.
受当代灌溉(技术设施)之赐，农作物在原来只有仙人掌和荞属科植物才能生存的地方旺盛的生长。
23、The development of mechanical timepieces spurred the search for more accurate sundials with which to regulate them.
机械计时器的发展促使人们寻求更精确的日晷，以便校准机械计时器。
24、Anthropology is a science in that anthropologists use a rigorous set of methods and techniques to document observations that can be checked by others.
人类学是一门科学，因为人类学家采用一整套强有力的方法和技术来记录观测结果，而这样记录下来的观测结果是供他人核查的。
25、Fungi are important in the process of decay, which returns ingredients to the soil, enhances soil fertility, and decomposes animal debris.
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。
26、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。
27、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。
28、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。
29、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。
30、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。
31、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。
32、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。
33、By the middle of the twentieth century, painters and sculptors in the United States had begun to exert a great worldwide influence over art.
到了二十一世纪中叶，美国画家和雕塑家开始在世界范围内对艺术产生重大影响。
34、In the eastern part of New Jersey lies the city of Elizabeth, a major shipping and manufacturing center.
伊丽莎白市，一个重要的航运和制造业中心，坐落于新泽西州的东部。
35、Elizabeth Blackwell, the first woman medical doctor in the United States, founded the New York Infirmary, an institution that has always had a completely female medical staff.
Elizabeth Blackwell，美国第一个女医生，创建了员工一直为女性纽约诊所。
36、Alexander Graham Bell once told his family that he would rather be remembered as a teacher of the deaf than as the inventor of the telephone.
Alexander Graham Bell曾告诉家人，他更愿意让后人记住他是聋子的老师，而非电话的发明者。
37、Because its leaves remain green long after being picked, rosemary became associated with the idea of remembrance.
采摘下的迷迭香树叶常绿不衰，因此人们把迷迭香树与怀念联系在一起。
38、Although apparently rigid, bones exhibit a degree of elasticity that enables the skeleton to withstand considerable impact.
骨头看起来是脆硬的，但它也有一定的弹性，使得骨骼能够承受相当的打击。
39、That xenon could not FORM chemical compounds was once believed by scientists.
科学家曾相信：氙气是不能形成化合物的。
40、Research into the dynamics of storms is directed toward improving the ability to predict these events and thus to minimize damage and avoid loss of life.
对风暴动力学的研究是为了提高风暴预测从而减少损失，避免人员伤亡。