【正文】 and, in areas of greater rainfall, the planting of long “shelter belts” of trees to break the force of the wind. Dry spells in the 1950s, 39。病毒的蛋白質(zhì)外殼 衣殼組成成分較復(fù)雜，上面有各種不 同類（如圖 :HIV 病毒 艾滋病病毒）型的受體，多糖等。酵母可以用于制作面食和釀酒 (酵母在無(wú)氧的環(huán)境下可以把葡萄糖轉(zhuǎn)變?yōu)榫凭?,而面粉中或多或少都有一些葡萄糖 ,所以放久了的面團(tuán)會(huì)有酒味 ),曲霉也可以用于釀造業(yè) 。 細(xì)菌分三類：種類最多的桿菌 （一般 110 微米）；數(shù)目眾多的球菌（一般 1 微米）以及纖細(xì)活潑的螺旋菌（見照片，一般長(zhǎng) 1020 微米，直徑 微米）。包括病毒、立克茨體、支原體、衣原體、細(xì)菌、放線菌、真菌中的霉菌、酵母菌和螺旋體等，也有將微植物和微動(dòng)物納入到其中的。 地外行星：火星到冥王星。 托福聽力背景知識(shí) (五 ) Rainforest Layers High temperature and rainfall production, more or less uniform throughout the year, characterize the rainforest worldwide. The water that is required to maintain this environment also threatens its existence. If left uncontrolled, the water that constantly bombards the soil would leech out most of the valuable nutrients. Plants and animals in this environment have developed adaptations to deal with the constant deluge and to pete successfully for nutrients. A closer look at the rainforest reveals that it is actually posed of four layers or munities. Each layer has a unique set of environmental conditions and anisms adapted to them. Read the descriptions below and watch for these layers and the infinite variety of life forms that occupy them as you visit La Selva. The Emergent Layer The tallest trees are the emergents, towering as much as 200 feet (60 m) above the forest floor with trunks that measure up to 16 feet (5 m) around. These huge trunks are usually supported by buttress roots to brace against the high winds. Most of these trees are broadleaved, hardwood evergreens. They are exposed to greater fluctuations of temperature, wind and rainfall than are their smaller panions. To hold water, leaves often have thick, waxy layers. Emergents may take advantage of the greater air movement above the canopy by developing winged seeds or fruits that are dispersed by wind to other parts of the forest. Sunlight is plentiful and animals such as eagles, monkeys, butterflies, insecteating bats and snakes inhabit this layer, some never venturing below it. The Canopy The primary layer of the rainforest, the canopy, extends beneath the emergents, rising to 150 feet (45m). Most canopy trees have smooth, oval leaves that e to a point. A possible explanation for this adaptation is that they shed rain quickly, discouraging the growth of lichens and mosses. In cloud forests such as La Selva, the canopy is lower and more dense, formed by smaller trees with twisted crowns of tiny, leathery leaves. At these higher elevations, the leaves have developed a highly reflective property that protects them from the higher levels of intense radiation. This almost solid green shield filters out 80% of the light, preventing its transmission to the forest below. Photosynthesis is everywhere. Flowers and fruits abound. Many species flower simultaneously, aiding crosspollination. In some species, flowers are produced on the trunks, making it easier for bat pollinators to find their way to the flowers. Monkeys, sloths, bats, treefrogs, ants, beetles, parrots, hummingbirds and snakes, to mention a few, can be found here, often never touching the ground during their lifetime. Epiphytes, some 28,000 species worldwide, use every tree surface as a place to live. Hollow trunks of trees and pools of water in bromeliads often are micromunities within the Canopy. The Understory This area gets only 25% of the sunlight available to the canopy. This limited light encourages the plant residents to devise unique ways to survive, such as the solarcollecting dark green leaves. Plants that survive in the understory include dwarf palms and softstalked species of families, such as the ginger family, acanthus and prayer plant or Maranta. These plants seldom grow to more than 12 feet ( m) in height. Understory plants have a more difficult time with pollination because of the lack of air movement. Most rely on insects. Some produce strong smelling flowers, others produce flowers and fruit on their trunks. This phenomenon, known as cauliflory, makes them more conspicuous to aid the process of pollination and seed dispersal. Many animals live here, including snakes, frogs, parakeets, leopards or jaguars and the largest concentration of insects. The Forest Floor Almost no plants grow in this region of 02% light and 100% humidity. The few flowering plants that live here tolerate deep shade. The floor itself is covered with a litter of rapidly deposing vegetation and anisms that break down into usable nutrients. A leaf that might take one year to depose in a temperate climate, will disappear in just six weeks on the rainforest floor. A high proportion of the nutrients in the system are locked in the large biomass (trees and other plant storage systems). There is heavy petition for these nutrients. This is why many trees are so shallowrooted. Large mammals, such as tapirs, forage for roots and tubers. Insects, including termites, cockroaches, beetles, centipedes, millipedes, scorpions and earthworms, along with the fungi, use the anic litter as a source of food. 托福聽力背景知識(shí) (六 ) 太陽(yáng)系的行星 九大行星通常按以下幾個(gè)方法分類： 根據(jù)組成： 固態(tài)的由石頭構(gòu)成的行星：水星，金星，地球和火星： 固態(tài)行星主要由巖石與金屬構(gòu)成，高密度，自轉(zhuǎn)速度慢，固態(tài)表面，沒有光環(huán)，衛(wèi)星較少。例如，黑洞有“隱身術(shù)”，人們無(wú)法直接觀察到它，連科學(xué)家都 只能對(duì)它內(nèi)部結(jié)構(gòu)提出各種猜想。而恒星的半徑越小，它對(duì)周圍的時(shí)空彎曲作用就越大，朝 某些角度發(fā)出的光就將沿彎曲空間返回恒星表面。汞被魚吸收富集，再通過食物鏈轉(zhuǎn)到貓和人的體內(nèi)。日本的水俁病，就是在大腦中累積了甲基汞，損害腦組織所致。地殼中汞的平均豐度為，土壤中為 ～ ，大氣中為 ～。古希臘曾經(jīng)光耀世界。 他們?cè)诮?jīng)過一個(gè)海峽時(shí)，又被女魔西拉抓走 6 個(gè)同伴。奧德修斯用酒灌醉巨人，削尖一根巨大的木桿，用火烤熱后，和 4 名同伴一起捅瞎了巨人的獨(dú)眼，得以逃生。因此，直到現(xiàn)在，歐洲人還把 “致命傷”叫做“阿基里斯的腳跟”。其中主將阿基里斯驍勇善戰(zhàn)，伊薩卡島的國(guó)王奧德修斯留下美麗的妻子皮娜洛普和剛出生的兒子特勒馬卡斯，也加入了希臘聯(lián)軍。參加喜宴的天后赫拉、智慧女神雅典娜、愛與美之神阿芙羅狄蒂（即羅馬神話中的維納斯）都認(rèn)為自己是美麗的，應(yīng)該得到這個(gè)金蘋果，于是爭(zhēng)吵起來(lái)。天神宙斯無(wú)法，只得讓她們?nèi)ヌ芈逡?，讓特洛伊王子帕里斯判定金蘋果該給誰(shuí)。 《伊利亞特》正是從戰(zhàn)爭(zhēng)的第 10 年初開始描寫的。之后，帕里斯也被希臘弓箭手射死。