某研究者为探讨脂肪摄入量与男性前列腺癌的关系，在社区内选择高脂肪和低脂肪摄入者各200名，从50岁开始对他们随访10年，在随访期间，高脂肪摄入组中有20人、低脂肪摄入者10人被诊断患有前列腺癌。
这种研究方法是（）
A.病例对照研究
B.队列研究
C.临床试验研究
D.理论流行病学研究
E.现况调查研究
参考答案：B
解析：队列研究是指根据是否暴露于所研究的因素，将研究对象分组，前瞻性观察它们的发病水平有误差别。本研究按有无高脂肪饮食分为高脂肪摄入组和低脂肪摄入组，前瞻性观察10年，看两组之间发病率有无差别，应属于队列研究。相对危险度=（a/n1）÷（c/n0）=（20/200）÷（10/200）=2.0。
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| More than twenty tons of ivory (象牙), seized from illegal hunters, was burned in Kenya to keep the ivory off the international market and to discourage the illegal killing of elephants for their ivory. The past 12 months had seen a record number of large ivory seizures across the world, a wildlife protection organization said Thursday, saying it had been a horrible year for elephants. There were at least 13 large seizures in 2011, totalling at least 23 tons of ivory meaning that about 2,500 elephants were killed. This compares to just six large seizures in 2010, weighing a total of just under 10 tons, and confirms a sharp rise in the trade since 2007. This is the worst year ever for large ivory seizures in the past 23 years-2011 had truly been a horrible year for elephants. Most illegal shipments of African elephant ivory end up in either China, where it is made into powder and used in traditional medicine, or in Thailand, with Malaysia the most frequent transit country (中转 国). The increasing quantities of ivory being traded, most of which are from either Kenyan or Tanzanian ports, reflected a rising demand in Asia. They constantly change their transport ways to Asia to avoid detection, including switching from airplanes to seaships, and once the ivory products arrive, their documentation (证明文件) is rewritten to hide the fact that they came from Africa. As most large ivory seizures fail to result in any arrests, the criminals are winning and have illegally made large amounts of money. International trade in elephant ivory was banned in 1990, and ETIS (the Elephant Trade Information System) holds the details of reports on more than 17,000 ivory and other elephant product seizures across the world since then.
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