2017公共英语五级阅读全真模拟试题.docx

2017公共英语五级阅读全真模拟试题Part BIn the following article some paragraphs have been removed. For Questions 66 70, choose the most suitable paragraph from the list A F to fit into each of the numbered gaps. There is one paragraph which does not fit in any of the gaps. Mark your answers on ANSWER SHEET 1.According to the American Academy of Dermatology, an estimated 10 to 50 million people in this country have an allergic reaction to poison ivy each year. Poison ivy is often very. difficult to spot. It closely resembles several other common garden plates, and can also blend in with other plants and weeds. But if you come into contact with it, you II soon know by the itchy, blistery rash that forms on your skin. Poison ivy is a red, itchy rash caused by the plant that bears its name. Many people get it when they are hiking or working in their garden and accidentally come into direct contact with the plant s leaves, roots, or stems. The poison ivy rash often looks like red lines, and sometimes it forms blisters.66.About 85 percent of people are allergic to the urushiol in poison ivy, according to the American Academy of Dermatology. Only a tiny amount of this chemical-1 billionth of a gram-is enough to cause a rash in many peo- ple. Some people may boast that they ve been exposed to poison ivy many times and have never gotten the rash, but that doesn t necessarily mean they re not allergic. Sometimes the allergy doesn t emerge until you ve been ex- posed several times, and some people develop a rash after their very first exposure. It may take up to ten days for the rash to emerge the first time.67.Here are some other ways to identify the poison ivy plant. It generally grows in a cluster of low, weed-like plants or a woody vine which can climb trees or fences. It is most often found in moist areas, such as riverbanks, woods, and pastures. The edges of the leaves are generally smooth or have tiny teeth. Their color changes based on the season-reddish in the spring; green in the summer; and yellow, orange, or red in the fall. Its berries are typically white.68.The body s immune system is normally in the business of protecting us from bacteria, viruses, and the foreign invaders that can make us sick. But when urushiol from the poison ivy plant touches the skin, it instigates an immune response, called dermatitis, to what would otherwise be a harmless substance. Hay fever is another example of this type of response; in the case of hay fever, the immune system overreacts to pollen, or another plant-produced substance.69.The allergic reaction to poison ivy is known as delayed hypersensitivity. Unlike immediate hypersensitivity, which causes an allergic reaction within minutes of exposure to an antigen, delayed hypersensitivity reactions don t emerge for several hours or even days after the exposure.70.In the places where your skin has come into contact with poison ivy leaves or urushiol, within one to two days you 11 develop a rash, which will usually itch, redden, bum, swell, and form blisters. The rash should go away within a week, but it can last longer. The severity of the reaction often has to do with how much urushiol youve touched. The rash may appear sooner in some parts of the body than in others, but it doesn t spread the urushiol simply absorbs into the skin at different rates in different parts of the body. Thicker skin such as the skin on the solesA. Because urushiol is found in all parts of the poison ivy plant-the leaves, stems, and roots-it s best to avoid the plant entirely to prevent a rash. The trouble is, poison ivy grows almost everywhere in the United States (with the exception of the Southwest, Alaska, and Hawaii), so geography won t help you. The general rule to identify poison ivy, leaflets three, let it be, doesn t always apply. Poison ivy usually does grow in groups of three leaves, with a longer middle leaf-but it can also grow with up to nine leaves in a group.B. Most people don t have a reaction the first time they touch poison ivy, but develop an allergic reaction after repeated exposure. Everyone has a different sensitivity, and therefore a slightly different reaction, to poison ivy. Sensitivity usually decreases with age and with repeat exposures to the plant.C. Here s how the poison ivy response occurs. Urushiol makes its way down through the skin, where it is metabolized, or broken down. Immune cells called T lymphocytes ( or T-cells) recognize the urushiol derivatives as a foreign substance, or antigen. They send out inflammatory signals called cytokines, which bring in white blood cells. Under orders from the cytokines, these white blood cells turn into macrophages. The macrophages eat foreign substances, but in doing so they also damage normal tissue, resulting in the skin inflammation that occurs with poison ivy.D. Poison ivy s cousins, poison oak and poison sumac, each have their own unique appearance. Poison oak grows as a shrub (one to six feet tall). It is typically found along the West Coast and in the South, in dry reas such fields, woodlands, and thickets. Like poison ivy, the leaves of poison oak are usually clustered in groups of three. They tend to be thick, green, and hairy on both sides. Poison sumac mainly grows in moist, swampy areas in the Northeast, Midwest, and along the Mississippi River. It is a woody shrub made up of stems with rows of seven to thirteen smooth-edged leaflets.E. The culprit behind the rash is a chemical in the sap of poison ivy plants called umshiol. Its name comes from the Japanese word urushi, meaning lacquer. Urushiol is the same substance that triggers an allergic reaction when people touch poison oak and poison sumac plants. Poison ivy, Eastern poison oak, Western poison oak, and poison sumac are all members of the same family-Anacardiaceae.F. Call your doctor if you experience these more serious reactions :Pus around the rash (which could indicate an infection).A rash around your mouth, eyes, or genital area.A fever above 100 degrees.A rash that does not heal after a week.PartB(每小题2分。共计l0分)短文赏析美国皮肤病学研究会报道，每年该国有1，000-5000万人口对毒藤产生过敏反应。本文讲述了毒藤是如何使人产生过敏反应的。由于毒藤跟公园里的普通植物及其相似，很难被辨认。许多人过敏都是在远足时或在花园里工作时，不经意间接触了这类植物的叶子、根茎和枝干引起的。毒藤疹会使皮肤瘙痒，呈红色带状，有时还会形成水泡。根本原因是毒藤中含有的一种叫urushiol的化学物质。尽管有时