1. Typical of the grassland dwellers of the continent is the American antelope， or pronghorn.

2. Of the millions who saw Haley's comet in 1986， how many people will live long enough to see it return in the twenty-first century.

3. Anthropologists have discovered that fear， happiness， sadness， and surprise are universally reflected in facial expressions.

4. Because of its irritating effect on humans， the use of phenol as a general antiseptic has been largely discontinued.

5. Insgroupsto remain in existence， a profit-making organization must， in the long run， produce something consumers consider useful or desirable.

6. The greater the population there is in a locality， the greater the need there is for water， transportation， and disposal of refuse.

7. It is more difficult to write simply， directly， and effectively than to employ flowery but vague expressions that only obscure one's meaning.

8. With modern offices becoming more mechanized， designers are attempting to personalize them with warmer， less severe interiors.

9. The difference between libel and slander is that libel is printed while slander is spoken.

10. The knee is the jointswheresthe thigh bone meets the large bone of the lower leg.

11. Acids are chemical compounds that， in water solution， have a sharp taste， a corrosive action on metals， and the ability to turn certain blue vegetable dyes red.

12. Billie Holiday's reputation as a great jazz-blues singer rests on her ability to give emotional depth to her songs.

13. Essentially， a theory is an abstract， symbolic representation of what is conceived to be reality.

14. Long before children are able to speak or understand a language， they communicate through facial expressions and by making noises.

15. Thanks to modern irrigation， crops now grow abundantly in areasswheresonce nothing but cacti and sagebrush could live.

16. The development of mechanical timepieces spurred the search for more accurate sundials with which to regulate them.

17. Anthropology is a science in that anthropologists use a rigorous set of methods and techniques to document observations that can be checked by others.

18. Fungi are important in the process of decay， which returns ingredients to the soil， enhances soil fertility， and decomposes animal debris.

19. When it is struck， a tuning fork produces an almost pure tone， retaining its pitch over a long period of time.

20. Although pecans are most plentiful in the southeastern part of the United States， they are found as far north as Ohio and Illinois.

希望以上20句对各位考生有助。小编祝大家托福写作考出理想的成绩!