流行病学病因的定义是（）
A.只要疾病发生，必然有病因存在
B.病因存在，必然引起疾病
C.造成机体器质性改变的因素
D.引起疾病发生概率升高的因素
E.导致疾病发生的许多因素
参考答案：D
解析：此题是理解判断题，考查考生对流行病学病因的理解。流行病学中对于病因的定义是指那些能使人群发病概率升高的因素，其中某个或多个因素不存在时，人群疾病频率就会下降。
| 阅读理解。 | ||
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| 1. Which of the following information about the plane Lowcarbon is NOT true? | ||
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| A. It can fly at 70 km an hour. B. It is solar -powered. C. It has passed a night-flight test. D. It is slower than a car. | ||
| 2. Lowcarbon is a special plane because ______. | ||
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| A. it's made in Switzerlland B. it has travelled around the world C. it can do turns in the sky D. it's big and light, but uses little enegy | ||
| 3. The purpose of the second article is to ______. | ||
[ ] | ||
| A. encourage us to visit Shanghai Expo B. ask us to be volunteers for Shanghai Expo C. invite us to write stories about Shanghai Expo D. tell us to get the lucky prize of Shanghai Expo | ||
| 4. Your stories about the 2010 Shanghai Expo for China Daily ______. | ||
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| A. can be in Chinese B. don't need to have photos C. must be given by post D. should be handed in by e-mail |