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抗原致敏的T细胞可以特异地杀伤、溶解带有相应抗原的肿瘤细胞，并受组织相容性抗原（MHC）限制。CD8+细胞毒性T细胞受________限制， CD4+辅助性T细胞受________限制。
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肿瘤的发生和演进是一个简单的生物学过程，涉及多因素的作用、多基因的参与和多阶段的演变。（）
For four days in hilly fields near this country town, thousands of men will wear brocaded wool uniforms in the summer heat, smoke smelly cheroots by camp fires, pitch canvas tents, eat dried beef — and wage war. Some 5,000 weekend warriors plan to reenact the first major battle of the American Civil War not far from where it took place, 48 kilometers west of Washington 125 years ago. The American Civil War Commemorative Committee of Culpeper, Virginia, the event’s sponsor, bills this as the biggest battle reenactment ever held in the United States. While the real north-south clash was fought out in one day, on July 21,1861, the replay will stretch out over four, including preliminary encampment, from July 17—20. Those arranging the rerun of the first Battle of Manassas, as Southerners call it the Battle of Bull Run to Northerners, expect over 50,000 Civil War buffs to watch the fighting roll across a 200-hectare tract. Some 1,500 artillery shells and a half million rounds of small-arms ammunition will be fired in the mock battle. A special effects company is arranging to set off explosions across the landscape, Hollywood war-film fashion, in counterpoint to thunderous fire cannons, some of which were used in the original battle. Jack Thompson, a director of the sponsoring committee, says dozens of mock Civil War military units have been created since interest was fanned in the 1960s when reenactments took place on a smaller scale to commemorate the war’s centenary. He said these groups, mostly in the south but with delegations from areas as far off as Scotland, Ireland and West Germany, strive to duplicate the uniforms, weapons and lifestyles of 1860s. Organiser Nancy Niero says everything has to be original, or reproduced as precisely as possible. Most authentic Civil War uniforms are too worn, too delicate or too small to fit the modern man, but some of the distinctive originals have been lovingly preserved and now serve as models for exact replicas. Cheating will be barred. That means a ban on using any sort of clothing, equipment, food or drink which did not exist during the real Civil War. Smokers, for instance, must shun cigarettes. Canned beer, soda and pre packed food are all out, but a spokeswoman said, "I guess if anyone gets hurt, we’ll use antibiotics. We won’t use leeches.\ Which of the following statements is implied but NOT stated in the passage
After the Anasazi abandoned southwestern Colorado in the late 1200s or early 1300s, history’s pages are blank. The Anasazi were masons and apartment builders who occupied the deserts, river valleys, and mesas of this region for over a thousand years, building structures that have weathered the test of time. The first Europeans to visit southwestern Colorado were the ever- restless, ambitious Spanish, who sought gold, pelts, and slaves. In1765, under orders from the Spanish governor in Santa Fe, Juan Maria Antonio Rivera led a prospecting and trading party into the region. Near the Dolores River in southwestern Colorado, he found some insignificant silver-bearing rocks, and it is thought that it was he who named the mountains nearby the Sierra de la Plata or the Silver Mountains. Rivera found little of commercial value that would interest his superiors in Santa Fe, but he did open up a route that would soon lead to the establishment of the Old Spanish Trail. This expedition and others to follow left names on the land which are the only reminders we have today the Spanish once explored this region. In 1776, one of the men who had accompanied Rivera, Andre Muniz, acted as guide for another expedition. That party entered southwestern Colorado in search of a route west to California, traveling near today’s towns of Durango and Dolores. Along the way, they camped at the base of a large green mesa which today carries the name Mesa Verde. They were the first Europeans to record the discovery of an Anasazi archaeological site m southwestern Colorado. By the early 1800s, American mountain men and trappers were exploring the area in their quest for beaver pelts. Men like Peg-leg Smith were outfitted with supplies in the crossroads trapping town of Taos, New Mexico. These adventurous American trappers were a tough bunch. They, possibly more than any other newcomers, penetrated deeply into the mountain fastness of southwestern Colorado, bringing back valuable information about the area and discovering new routes through the mountains. One of the trappers, William Becknell, the father of the Santa Fe Trail, camped in the area of Mesa Verde, where he found pottery shards, stone houses, and other Anasazi remains. What do we know about the 1776 expedition
In the last five years prices for western art have soared. Popular artists can’t paint fast enough to keep up with the demand for paintings that regularly sell for $30,000 to $50,000. The boom is all the more striking considering that 20 years ago western art had virtually no market at all. To some extent, its success reflects Americans’ increased interest in their heritage. Certainly there are those who would argue that western art is the truly indigenous American art. Its roots date back at least as far as the early 19th century, when George Catlin, perhaps the greatest western artist of that period, took his paints and brushes and ventured into the wilderness in the company of William Clark. His close observations of the beautifully savage country molded a new and powerful aesthetic, one that incorporated the sweep of plains and the primitive dynamism of the people who lived there. Catlin’s portraits of Indian chiefs are noble, his paintings of scenes such as "Buffalo Hunt with Bows and Arrows" are full of action and bravery, and for all the smallness of the canvas, they have tremendous scope. Frederic Remington and Charles Russell continued the tradition of painter as historian into the early 1900s. Their dramatic — some critics say melodramatic narrative art found an overwhelming public sympathy. Today when people speak of western art they mean realistic art with western subject matter, past and present. In the forefront are those who call themselves cowboy artists, and many of the elite of this group are members of the Cowboy Artists of America, whose first objective is "to perpetuate the memory and culture of the Old West." Not surprisingly, they paint cowboys and, by extension, indians and mountain men, but not landscapes and animal pictures. Cowboy Artists blend a romantic vision of the Old West with a historically accurate depiction of that way of life; every saddle girth is tied correctly; every feather in an Indian’s war bonnet is in place and of the proper species. In Howard Terpning’s "The Victors", for instance, an anthropologist could tell by the warriors’ clothing which tribe they belonged to. Many critics today refuse to recognize western art as art. In a real sense, it is, as in the days of Remington and Russell, a popular movement-a middle- class phenomenon. And why not Cowboy art is unequivocally stating middle- class values. In the west, "middle class" isn’t a derogatory term. It’s almost synonymous with America. Just as these people are unabashedly patriotic, they want their art to reflect their values of striving and prospering, of optimism and individualism. The paintings of Cowboy Artists are distinguished
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