2016年托福阅读理解冲刺练习题及答案

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2016年托福阅读理解冲刺练习题及答案

　　text 1

2016年托福阅读理解冲刺练习题及答案

　　Plants are subject to attack and infection by a remarkable variety of symbiotic species and have evolved a diverse array of mechanisms designed to frustrate the potential colonists. These can be divided into preformed or passive defense mechanisms and inducible or active systems. Passive plant defense comprises physical and chemical barriers that prevent entry of pathogens, such as bacteria, or render tissues unpalatable or toxic to the invader. The external surfaces of plants, in addition to being covered by an epidermis and a waxy cuticle, often carry spiky hairs known as trichomes, which either prevent feeding by insects or may even puncture and kill insect larvae. Other trichomes are sticky and glandular and effectively trap and immobilize insects.

　　If the physical barriers of the plant are breached, then preformed chemicals may inhibit or kill the intruder, and plant tissues contain a diverse array of toxic or potentially toxic substances, such as resins, tannins, glycosides, and alkaloids, many of which are highly effective deterrents to insects that feed on plants. The success of the Colorado beetle in infesting potatoes, for example, seems to be correlated with its high tolerance to alkaloids that normally repel potential pests. Other possible chemical defenses, while not directly toxic to the parasite, may inhibit some essential step in the establishment of a parasitic relationship. For example, glycoproteins in plant cell walls may inactivate enzymes that degrade cell walls. These enzymes are often produced by bacteria and fungi.

　　Active plant defense mechanisms are comparable to the immune system of vertebrate animals, although the cellular and molecular bases are fundamentally different. Both, however, are triggered in reaction to intrusion, implying that the host has some means of recognizing the presence of a foreign organism. The most dramatic example of an inducible plant defense reaction is the hypersensitive response. In the hypersensitive response, cells undergo rapid necrosis — that is, they become diseased and die — after being penetrated by a parasite; the parasite itself subsequently ceases to grow and is therefore restricted to one or a few cells around the entry site. Several theories have been put forward to explain the basis of hypersensitive resistance.

　　1. What does the passage mainly discuss?

　　(A) The success of parasites in resisting plant defense mechanisms

　　(B) Theories on active plant defense mechanisms

　　(D) How the immune system of animals and the defense mechanisms of plants differ

　　2. The phrase "subject to" in line 1 is closest in meaning to

　　(A) susceptible to

　　(B) classified by

　　(D) strengthened by

　　3. The word "puncture穿刺" in line 8 is closest in meaning to

　　(A) pierce

　　(B) pinch

　　(D) cover .

　　4. The word "which" in line 12 refers to

　　(A) tissues

　　(B) substances 物质

　　(D) insects

　　5. Which of the following substances does the author mention as NOT necessarily being toxic to the Colorado beetle?

　　(A) resins

　　(B) tannins

　　(D) alkaloids

　　6. Why does the author mention "glycoproteins" in line 17?

　　(A) to compare plant defense mechanisms to the immune system of animals

　　(B) to introduce the discussion of active defense mechanisms in plants

　　(D) to emphasize the importance of physical barriers in plant defense

　　7. The word "dramatic引人注目的，戏剧性的" in line 23 could best be replaced by

　　(A) striking

　　(B) accurate

　　(D) appealing

　　8. Where in the passage does the author describe an active plant-defense reaction?

　　(A) Lines 1-3

　　(B) Lines 4-6

　　(D) Lines 24-27

　　9. The passage most probably continues with a discussion of theories on

　　(A) the basis of passive plant defense

　　(B) how chemicals inhibit a parasitic relationship.

　　(D) the principles of the hypersensitive response

　　参考答案

　　1-9 CAABD CADD

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　　Among the species of seabirds that use the windswept cliffs of the Atlantic coast of Canada in the summer to mate, lay eggs, and rear their young are common murres, Atlantic puffins, black-legged kittiwakes, and northern gannets. Of all the birds on these cliffs, the black-legged kittiwake gull is the best suited for nesting on narrow ledges. Although its nesting habits are similar to those of gulls that nest on flat ground, there are a number of important differences related to the cliff-nesting habit.

　　The advantage of nesting on cliffs is the immunity it gives from foxes, which cannot scale the sheer rocks, and from ravens and other species of gulls, which have difficulty in landing on narrow ledges to steal eggs. This immunity has been followed by a relaxation of the defenses, and kittiwakes do not react to predators nearly as fiercely as do ground-nesting gulls. A colony of Bonaparte's gulls responds to the appearance of a predatory herring gull by flying up as a group with a clamor of alarm calls, followed by concerted mobbing, but kittiwakes simply ignore herring gulls, since they pose little threat to nests on cliffs. Neither do kittiwakes attempt to conceal their nest. Most gulls keep the nest area clear of droppings, and remove empty eggshells after the chicks have hatched, so that the location of the nest is not given away. Kittiwakes defecate over the edge of the nest, which keeps it clean, but this practice, as well as their tendency to leave the nest littered with eggshells, makes its location very conspicuous.

　　On the other hand, nesting on a narrow ledge has its own peculiar problems, and kittiwake behavior has become adapted to overcome them. The female kittiwake sits when mating, whereas other gulls stand, so the pair will not overbalance and fall off the ledge. The nest is a deep cup, made of mud or seaweed, to hold the eggs safely, compared with the shallow scrape of other gulls, and the chicks are remarkably immobile until fully grown. They do not run from their nests when approached, and if they should come near to the cliff edge, they instinctively turn back.

　　1. What aspect of the kittiwake gull does the passage mainly discuss?

　　(A) Its defensive behavior

　　(B) It interactions with other gull species

　　(D) Its physical difference from other gull species

　　2. The word "rear抚养，培养" in line 2 is closest in meaning to

　　(A) visit

　　(B) watch

　　(D) raise

　　3. The word "scale攀爬" in line 8 is closest in meaning to

　　(A) climb

　　(B) avoid

　　(D) measure