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1、 模拟模拟 考生： 金币：0 考试时间：120 分钟 满分：100 分 英语四级新试题 21PartPart IIII ReadingReading ComprehensionComprehension (Skimming(Skimming andand Scanning)Scanning) Directions:Directions: InIn thisthis part,part, youyou willwill havehave 1515 minutesminutes toto gogo overover thethe passagepassage quicklyquickly anda
2、nd answeranswer thethe questionsquestions onon AnswerAnswer sheet1.sheet1. ForFor questionsquestions , , markmark Y Y (for(for YES)YES) ifif thethe statementstatement agreesagrees withwith thethe informationinformation givengiven inin thethe passage;passage; N N (for(for NO)NO) ifif thethe statement
3、statement contradictscontradicts thethe informationinformation givengiven inin thethe passage;passage; NGNG (for(for NOTNOT GIVEN)GIVEN) ifif thethe informationinformation isis notnot givengiven inin thethe passage.passage. ForFor questions,questions, completecomplete thethe sentencessentences withw
4、ith thethe informationinformation givengiven inin thethe passage.passage.Snake Venom What is it about snakes that mesmerize people? For thousands of years, these creatures have inspired religious myths, fanatical fear, and endless curiosity. Streamlined to the bare essentials -mouth, belly, brain, s
5、pine -snakes manage to slink over desert sands and rocky slopes as well as swim in rivers and glide through the rainforest canopy. In more than 100 million years on Earth, theyve evolved to elegant perfection. “The way a snake moves, through sleek body curves, light shining off its scales, is one of
6、 the most impressive sights nature has to offer,“ says cobra expert Wolfgang Wuster at the University of Wales. Apes climb with powerful arms and hands; frogs swim with webbed feet; falcons seize prey with sharp talons. Snakes merely with a backbone do all these things. Among them, the king cobras a
7、ggressive reputation and its lethal defenses have inspired people to view its powers as godlike. In India and Southeast Asia, societies have long revered cobras and king cobras and placed them at the center of their most sacred rites. The deadly weapon of king cobra is its fangs, almost half an inch
8、 (8-10 millimeters) long. Because they are fixed to the upper jaw, they have to be short. If they were longer, the king might bite the floor of its mouth and commit royal suicide. Angled back into the snakes mouth, the fangs help push the prey on its path to the stomach. A regal bite delivers venom
9、from glands attached to the fangs. The flexing of a small muscle forces the venom through the hollow fangs into the victim. Within minutes, neurotoxins stun the preys nervous system, especially the nervous impulses for breathing. Other toxins start digesting the paralyzed victim. Drop for drop, a ki
10、ng cobras venom is actually less lethal than a common cobras. The king more than makes up for it by delivering more venom per bite -as much as 0.2 fluid ounces (7 milliliters) of liquid. Thats enough to kill an elephant, or 20 people. Snake venom is produced by special cells in two large venom gland
11、s on each side of the head. Out of 3,000 known species of snakes, more than 500 are venomous. The 10 most lethal snakes in the world belong to the elapids -often called the cobra family. Cobra venom kills via neurotoxins, proteins that paralyze an animals nervous system and diaphragm, abdominal musc
12、les used to breathe. The snake metes out the exact amount of venom needed to suffocate the prey, then swallows its catch. The proteinaceous nature of snake venom was established by Napoleon Bonapartes brother, Lucien in 1843. Proteins constitute the major portion of venoms dry weight -90% or more. S
13、nake venom is a cocktail of hundreds, sometimes thousands, of different proteins and enzymes. Many of these proteins are harmless but a percentage of them are toxins. The makeup of these toxins varies widely from species to species. This complexity accounts for the widely differing effects of snakeb
14、ite. Meanwhile, venoms are also rich in hydrolithic enzymes, a complex mix of polypeptides, nucleases, peptidases, etc. , which help digest the snakes prey. Some of them also enhance or contribute to the toxic effect of the venom. As early as 1949 it was shown that an enzyme from the Bothrops specie
15、s produces a vasodilation resulting from the production of a hypotensor neuropeptide, bradykinin. This had important consequences for man leading to drugs for the control of blood pressure. Anti-venoms were first produced a century or more ago. Albert Calmette demonstrated that it was possible to “h
16、yper-immunize“ an animal against snakebite by graduated and increased regular dosage of that animal with the venom of that snake. He further demonstrated that a second animal could be saved after snakebite by introducing the serum of the immunized creature. This discovery is still the basis of the production of modern anti-venoms. A few modern modifications have been introduced -such as
