托福考试阅读冲刺

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托福考试阅读冲刺1

It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species' death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.

The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species became extinct at the same time — a mass extinction. One of the best-known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when approximately 95 percent of all species died, mass extinctions can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the oceans. Such a change would probably lead to a mass extinction.

One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth's orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species' survival may have nothing to do with its ability or inability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.

1. The word "it" in line 3 refers to

(A) environment

(B) species

(D) 99 percent

2. The word "ultimately" in line 8 is closest in meaning to

(A) exceptionally

(B) dramatically

(D) unfortunately

3. What does the author say in paragraph 1 regarding most species in Earth's history

(A) They have remained basically unchanged from their original forms.

(B) They have been able to adapt to ecological changes.

(D) They are no longer in existence.

4. Which of the following is NOT mentioned in paragraph 1 as resulting from rapid ecological change?

(A) Temperature changes

(B) Availability of food resources

(D) Competition among species

5. The word "demise" in line 12 is closest in meaning to

(A) change

(B) recovery

(D) death

6. Why is "plankton" mentioned in line 17?

(A) To demonstrate the interdependence of different species.

(B) To emphasize the importance of food resources in preventing mass extinction.

(D) To point out that certain species could never become extinct.

7. According to paragraph 2, evidence from fossils suggests that

(A) Extinction of species has occurred from time to time throughout Earth's history.

(B) Extinctions on Earth have generally been massive

(D) Dinosaurs became extinct much earlier than scientists originally believed.

8. The word "finding" in line 20 is closest in meaning to

(A) published information

(B) research method

(D) scientific discovery

9. Which of the following can be inferred about the theory mentioned in Line 21-23?

(A) Many scientists could be expected to disagree with it.

(B) Evidence to support the theory has recently been found.

(D) Most scientists believe the theory to be accurate.

10. In paragraph 3, the author makes which of the following statements about a species' survival?

(A) It reflects the interrelationship of many species.

(B) It may depend on chance events.

(D) It is associated with astronomical conditions.

11. According to the passage , it is believed that the largest extinction of a species occurred

(A) 26 million years ago

(B) 65 million years ago

(D) 250 million years ago

参考答案：BCDCD AADAB C

托福考试阅读冲刺2

Under the Earth's topsoil, at various levels, sometimes under a layer of rock, there are deposits of clay. Look at cuts where highways have been built to see exposed clay beds; or look at a construction site, where pockets of clay may be exposed. Rivers also reveal clay along their banks, and erosion on a hillside may make clay easily accessible. What is clay made of? The Earth's surface is basically rock, and it is this rock that gradually decomposes into clay. Rain, streams, alternating freezing and thawing, roots of trees and plants forcing their way into cracks, earthquakes, volcanic action, and glaciers — all of these forces slowly break down the Earth's exposed rocky crust into smaller and smaller pieces that eventually become clay.

Rocks are composed of elements and compounds of elements. Feldspar, which is the most abundant mineral on the Earth's surface, is basically made up of the oxides silica and alumina combined with alkalis like potassium and some so-called impurities such as iron. Feldspar is an essential component of granite rocks, and as such it is the basis of clay. When it is wet, clay can be easily shaped to make a variety of useful objects, which can then be fired to varying degrees of hardness and covered with impermeable decorative coatings of glasslike material called glaze. Just as volcanic action, with its intense heat, fuses the elements in certain rocks into a glasslike rock called obsidian, so can we apply heat to earthen materials and change them into a hard, dense material. Different clays need different heat levels to fuse, and some, the low-fire clays, never become nonporous and watertight like highly fired stoneware. Each clay can stand only a certain amount of heat without losing its shape through sagging or melting. Variations of clay composition and the temperatures at which they are fired account for the differences in texture and appearance between a china teacup and an earthenware flowerpot.

1. The author's main point in paragraph 1 is that clay deposits

(A) conceal layers of rock

(B) can be found in various places

(D) must be removed from construction sites

2. It can be inferred from the passage that clay is LEAST likely to be plentiful in which of the following areas?

(A) in desert sand dunes

(B) in forests

(D) near rivers

3. The word "accessible" in line 4 is closest in meaning to

(A) buried

(B) improved

(D) workable

4. According to the passage , rock breaks down into clay under all of the following conditions EXCEPT when

(A) it is exposed to freezing and thawing

(B) roots of trees force their way into cracks

(D) natural forces wear away the Earth's crust

5. Why does the author mention feldspar in line 10?

(A) It is often used as a substitute for clay.

(B) It is damaged by the oxides in clay.

(D) It is a major component of clay.

6. The word "it" in line 13 refers to

(A) iron

(B) feldspar

(D) clay

7. Based on the information in the passage , it can be inferred that low-fire clays are MOST appropriate for making objects that

(A) must be strong

(B) can be porous

(D) are highly decorated

8. The phrase "account for" in line 22 is closest in meaning to

(A) reduce

(B) explain

(D) list all of

9. The passage supports which of the following conclusions?

(A) Clay deposits are only found deep in the Earth.

(B) If clay contains too much iron it will melt when fired.

(D) If sufficient heat is applied, all clay will become nonporous.

参考试题：BACCD BBBC

托福考试阅读冲刺3

Many prehistoric people subsisted as hunters and gatherers. Undoubtedly, game animals, including some very large species, provided major components of human diets. An important controversy centering on the question of human effects on prehistoric wildlife concerns the sudden disappearance of so many species of large animals at or near the end of the Pleistocene epoch. Most paleontologists suspect that abrupt changes in climate led to the mass extinctions. Others, however, have concluded that prehistoric people drove many of those species to extinction through overhunting. In their "Pleistocene overkill hypothesis," they cite what seems to be a remarkable coincidence between the arrival of prehistoric peoples in North and South America and the time during which mammoths, giant ground sloths, the giant bison, and numerous other large mammals became extinct.

Perhaps the human species was driving others to extinction long before the dawn of history. Hunter-gatherers may have contributed to Pleistocene extinctions in more indirect ways. Besides overhunting, at least three other kinds of effects have been suggested: direct competition, imbalances between competing species of game animals, and early agricultural practices. Direct competition may have brought about the demise of large carnivores such as the saber-toothed cats. These animals simply may have been unable to compete with the increasingly sophisticated hunting skills of Pleistocene people.

Human hunters could have caused imbalances among game animals, leading to the extinctions of species less able to compete. When other predators such as the gray wolf prey upon large mammals, they generally take high proportions of each year's crop of young. Some human hunters, in contrast, tend to take the various age-groups of large animals in proportion to their actual occurrence. If such hunters first competed with the larger predators and then replaced them, they may have allowed more young to survive each year, gradually increasing the populations of favored species. As these populations expanded, they in turn may have competed with other game species for the same environmental niche, forcing the less hunted species into extinction. This theory, suggests that human hunters played an indirect role in Pleistocene extinctions by hunting one species more than another.

1. What does the passage mainly discuss?

(A) The effects of human activities on prehistoric wildlife

(B) The origins of the hunter-gatherer way of life

(D) The change in climate at the end of the Pleistocene epoch

2. The word "Undoubtedly" in line 1 is closest in meaning to

(A) occasionally

(B) unexpectedly

(D) certainly

3. The word "components" in line 2 is closest in meaning to

(A) parts

(B) problems

(D) varieties

4. Which of the following is mentioned as supporting the Pleistocene overkill hypothesis?

(A) Many of the animals that became extinct were quite large.

(B) Humans migrated into certain regions around the time that major extinctions occurred.

(D) Humans began to keep and care for certain animals.

5. The word "Besides" in line 14 is closest in meaning to

(A) caused by

(B) whereas

(D) in favor of

6. The author mentions saber-toothed cats in line 17 as an example of a carnivore that

(A) became extinct before the Pleistocene epoch

(B) was unusually large for its time

(D) caused the extinction of several species

7. The word "they" in line 22 refers to

(A) human hunters

(B) game animals

(D) large mammals

8. According to the passage , what is one difference between the hunting done by some humans and the hunting done by gray wolves?

(A) Some humans hunt more frequently than gray wolves.

(B) Gray wolves hunt in larger groups than some humans.

(D) Some humans prey on animals of all ages, but gray wolves concentrate their efforts on young animals.

9. The word "favored" in line 26 is closest in meaning to

(A) large

(B) escaping

(D) local

10. According to the passage , the imbalances discussed in paragraph 3 may have resulted from

(A) the effect of climate changes on large game animals

(B) large animals moving into a new environment

(D) older animals not being able to compete with younger animals

参考答案：ADABC CCDCC

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托福考试阅读冲刺

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