托福阅读真题Official 43 Passage 1（三）

托福阅读真题Official 43 Passage 1（三）

Seagrasses

Many areas of the shallow sea bottom are covered with a lush growth of aquatic flowering plants adapted to live submerged in seawater.These plants are collectively called seagrasses.Seagrass beds are strongly influenced by several physical factors.The most significant is water motion:currents and waves.Since seagrass systems exist in both sheltered and relatively open areas,they are subject to differing amounts of water motion.For any given seagrass system,however,the water motion is relatively constant.Seagrass meadows in relatively turbulent waters tend to form a mosaic of individual mounds,whereas meadows in relatively calm waters tend to form flat,extensive carpets.The seagrass beds,in turn,dampen wave action,particularly if the blades reach the water surface.This damping effect can be significant to the point where just one meter into a seagrass bed the wave motion can be reduced to zero.Currents are also slowed as they move into the bed.

The slowing of wave action and currents means that seagrass beds tend to accumulate sediment.However,this is not universal and depends on the currents under which the bed exists.Seagrass beds under the influence of strong currents tend to have many of the lighter particles,including seagrass debris,moved out,whereas beds in weak current areas accumulate lighter detrital material.It is interesting that temperate seagrass beds accumulate sediments from sources outside the beds,whereas tropical seagrass beds derive most of their sediments from within.

Since most seagrass systems are depositional environments,they eventually accumulate organic material that leads to the creation of fine-grained sediments with a much higher organic content than that of the surrounding unvegetated areas.This accumulation,in turn,reduces the water movement and the oxygen supply.The high rate of metabolism(the processing of energy for survival)of the microorganisms in the sediments causes sediments to be anaerobic(without oxygen)below the first few millimeters.According to ecologist J.W.Kenworthy,anaerobic processes of the microorganisms in the sediment are an important mechanism for regenerating and recycling nutrients and carbon,ensuring the high rates of productivity—that is,the amount of organic material produced—that are measured in those beds.In contrast to other productivity in the ocean,which is confined to various species of algae and bacteria dependent on nutrient concentrations in the water column,seagrasses are rooted plants that absorb nutrients from the sediment or substrate.They are,therefore,capable of recycling nutrients into the ecosystem that would otherwise be trapped in the bottom and rendered unavailable.

Other physical factors that have an effect on seagrass beds include light,temperature,and desiccation(drying out).For example,water depth and turbidity(density of particles in the water)together or separately control the amount of light available to the plants and the depth to which the seagrasses may extend.Although marine botanist W.A.Setchell suggested early on that temperature was critical to the growth and reproduction of eelgrass,it has since been shown that this particularly widespread seagrass grows and reproduces at temperatures between 2 and 4 degrees Celsius in the Arctic and at temperatures up to 28 degrees Celsius on the northeastern coast of the United States.Still,extreme temperatures,in combination with other factors,may have dramatic detrimental effects.For example,in areas of the cold North Atlantic,ice may form in winter.Researchers Robertson and Mann note that when the ice begins to break up,the wind and tides may move the ice around,scouring the bottom and uprooting the eelgrass.In contrast,at the southern end of the eelgrass range,on the southeastern coast of the United States,temperatures over 30 degrees Celsius in summer cause excessive mortality.Seagrass beds also decline if they are subjected to too much exposure to the air.The effect of desiccation is often difficult to separate from the effect of temperature.Most seagrass beds seem tolerant of considerable changes in salinity(salt levels)and can be found in brackish(somewhat salty)waters as well as in full-strength seawater

Question 5 of 14

According to paragraph 3,Plato believed that the ideal city-state should be

A.governed by a ruling body of about 5,000 city leaders with a total population of no more than 100,000

B.led by the most qualified individual

C.governed by the group of citizens with the most knowledge about the issues of the day

D.small enough so that everyone would know each other

正确答案：D

题目详解

题型分类：事实信息题

原文定位：根据Plato，ideal city-state可以定位到第三段的第四句。

选项分析：

D选项：第四句的意为哲学家柏拉图（428–348 B.C.）认为理想的城市国家应拥有大约5,000名公民，因为对于希腊人来说，社区中的每个人都应该相互认识很重要。因此，D选项正确。

A选项：意思为政府由大约5000名城市领导人组成的统治机构统治，总人口不超过10万人。无中生有。

B选项：原文并没有提到，与原文无关。

C选项：意思为由一群对每天的知识了解最多的公民管理。原文并没有提到，与原文无关。

Question 6 of 14

Why does the author mention“The philosopher Aristotle”?

A.To provide additional evidence that the ancient Greeks believed that political units must be small

B.To demonstrate the accuracy of philosophers’predictions about the end of the classical Greek city-state

C.To show how changes in the city-state system from the fifth to the third century B.C.were reflected in the ideas of its philosophers

D.To support the claim that small city-states were ideally suited to produce philosophical inquiry

正确答案：A

题目详解

题型分类：修辞目的题

原文定位：根据The philosopher Aristotle可以定位到第三段的第3句和最后一句。

选项分析：

A选项：第四句的意为哲学家柏拉图（428–348 B.C.）认为理想的城市国家应拥有大约5,000名公民，因为对于希腊人来说，社区中的每个人都应该相互认识很重要。最后一句意思为哲学家亚里斯多德生活在城市体系衰落的时代，他认为拥有10万个政治实体根本无法管理自己。因此，其目的为为小的unit提供了证据，即选项A为正确选项。

B选项：意思为以证明哲学家们关于古希腊城邦灭亡的预言是正确的，与柏拉图的观点无关。

C选项：意思为展示公元前5世纪至公元前3世纪城邦制度的变化如何反映在哲学家的思想中。与原文无关。

D选项：意思为支持小城邦最适合进行哲学探索的观点。与原文无关。