21、Essentially, a theory is an abstract, symbolic representation of what is conceived to be reality.
22、Thanks to modern irrigation, crops now grow abundantly in areas where once nothing but cacti and sagebrush could live.
23、The development of mechanical timepieces spurred the search for more accurate sundials with which to regulate them.
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.
25、Fungi are important in the process of decay, which returns ingredients to the soil, enhances soil fertility, and decomposes animal debris.
26、When it is struck, a tuning fork produces an almost pure tone, retaining its pitch over a long period of time.
27、Although pecans are most plentiful in the southeastern part of the United States, they are found as far north as Ohio and Illinois.
28、Eliminating problems by transferring the blame to others is often called scape-goating.
29、The chief foods eaten in any country depend largely on what grows best in its climate and soil.
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.
31、Most substance contract when they freeze so that the density of a substance’s solid is higher than the density of its liquid.
32、The mechanism by which brain cells store memories is not clearly understood.
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.
34、In the eastern part of New Jersey lies the city of Elizabeth, a major shipping and manufacturing center.
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.
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.
38、Although apparently rigid, bones exhibit a degree of elasticity that enables the skeleton to withstand considerable impact.
39、That xenon could not FORM chemical compounds was once believed by scientists.
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.