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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.
美國皮膚病學(xué)研究會報(bào)道，每年該國有1，000-5000萬人口對毒藤產(chǎn)生過敏反應(yīng)。本文講述了毒藤是如何使人產(chǎn)生過敏反應(yīng)的。由于毒藤跟公園里的普通植物及其相似，很難被辨認(rèn)。許多人過敏都是在遠(yuǎn)足時或在花園里工作時，不經(jīng)意間接觸了這類植物的葉子、根莖和枝干引起的。毒藤疹會使皮膚瘙癢，呈紅色帶狀，有時還會形成水泡。根本原因是毒藤中含有的一種叫urushiol的化學(xué)物質(zhì)。盡管有時候這種物質(zhì)很小量，許多人還是會過敏。文章介紹了毒藤的作用機(jī)理，告訴人們?nèi)绾巫R別毒藤。它通常生長在潮濕的地區(qū)：如河畔，森林及草原上。毒藤植物的邊緣通常來說是很滑的，或者有小齒，顏色會隨著季節(jié)的更替而變化。春天是淡紅色，夏天是綠色，秋季則會變?yōu)辄S色、橘色或紅色。不同的.人對毒藤的反應(yīng)時間和癥狀也是不一樣的。平時應(yīng)該多加注意，避免接觸毒藤。
66.e【解析】文章第一段講述了毒藤會使人過敏產(chǎn)生疹子，第三段提到85%的人對毒藤中的urushiol過敏，選項(xiàng)e介紹了urushiol一詞的來源，并且介紹了毒藤使人過敏的根本原因就是毒藤中含有這種化學(xué)物質(zhì)。所以本題應(yīng)選e。
67.a【解析l下面一段講的是其他方法來鑒別毒藤，所以看過選項(xiàng)之后，我們可以推斷出該空缺的是一些鑒別毒藤的方法，urushiol存在于毒藤的各個部分，最好避免接觸毒藤的任何一處。其存在于美國的各個州，三個葉子的肯定不是毒藤等信息。注意下一段的關(guān)鍵詞“other”。所以本題應(yīng)選a。
68.d【解析】該空承接上段，講的還是與毒藤相關(guān)的信息。毒橡樹跟毒漆樹的生長地點(diǎn)、環(huán)境及其形狀。還是對鑒別毒藤的支撐信息。所以本題應(yīng)選d。
69.c【解析】接下來講的是人體的免疫系統(tǒng)與毒藤之間的關(guān)系。毒藤會使人產(chǎn)生什么樣的反應(yīng)，該空緊接的就是毒藤過敏反應(yīng)是如何產(chǎn)生的?！癶ere’s how the poison ivy response occurs.”一句承上啟下。所以本題應(yīng)選c。
70.b【解析】該空缺之前講的是毒藤的過敏反應(yīng)是滯后的。不是馬上產(chǎn)生的。接下來的相關(guān)信息是不同的人敏感度不一樣，過敏反應(yīng)發(fā)生的時間也會不一樣。所以本題應(yīng)選b。
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