2017公共英语五级阅读全真模拟试题

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　　Part B

　　In 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 you've 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 soles

　　A. 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。尽管有时候这种物质很小量，许多人还是会过敏。文章介绍了毒藤的作用机理，告诉人们如何识别毒藤。它通常生长在潮湿的地区：如河畔，森林及草原上。毒藤植物的边缘通常来说是很滑的，或者有小齿，颜色会随着季节的更替而变化。春天是淡红色，夏天是绿色，秋季则会变为黄色、橘色或红色。不同的人对毒藤的反应时间和症状也是不一样的。平时应该多加注意，避免接触毒藤。

　　答案及解析

　　66.E【解析】文章第一段讲述了毒藤会使人过敏产生疹子，第三段提到85%的人对毒藤中的urushiol过敏，选项E介绍了urushiol一词的来源，并且介绍了毒藤使人过敏的根本原因就是毒藤中含有这种化学物质。所以本题应选E。

　　67.A【解析l下面一段讲的是其他方法来鉴别毒藤，所以看过选项之后，我们可以推断出该空缺的是一些鉴别毒藤的方法，urushiol存在于毒藤的各个部分，最好避免接触毒藤的任何一处。其存在于美国的各个州，三个叶子的肯定不是毒藤等信息。注意下一段的关键词“other”。所以本题应选A。

　　68.D【解析】该空承接上段，讲的还是与毒藤相关的信息。毒橡树跟毒漆树的生长地点、环境及其形状。还是对鉴别毒藤的支撑信息。所以本题应选D。

　　69.c【解析】接下来讲的是人体的免疫系统与毒藤之间的关系。毒藤会使人产生什么样的反应，该空紧接的就是毒藤过敏反应是如何产生的。“Here’S how the poison ivy response OCCURS.”一句承上启下。所以本题应选C。

　　70.B【解析】该空缺之前讲的是毒藤的过敏反应是滞后的。不是马上产生的。接下来的相关信息是不同的人敏感度不一样，过敏反应发生的时间也会不一样。所以本题应选B。

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