问题
问答题 简答题
何谓致癌因素?有哪些重要的外源性致癌因素?
答案
参考答案：
凡能引起癌症的病因称为致癌因素，分外源性和内源性两大类。目前受到重视的外源性致癌因素有：①物理性致癌因素：如电离辐射、紫外线及异物等；②化学性致癌因素：如3，4-苯并芘、亚硝胺等；③生物性致癌因素：其中最重要的是病毒致癌。
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何谓致癌因素?有哪些重要的外源性致癌因素?
参考答案：
凡能引起癌症的病因称为致癌因素，分外源性和内源性两大类。目前受到重视的外源性致癌因素有：①物理性致癌因素：如电离辐射、紫外线及异物等；②化学性致癌因素：如3，4-苯并芘、亚硝胺等；③生物性致癌因素：其中最重要的是病毒致癌。
Photographs are everywhere , They decorate the walls of homes and are used in stores for sales of different goods. The news is filled with pictures of fires, floods and special events, 71 They can also bring things close that are far away. Through photos, people can see wild animals, cities in foreign lands and even the stars in outer space . Photos also tell stories. Reporting the news through photos is called photojournalism. At times photojournalists tell their stories through a single picture. At other times, they use a group of pictures to tell a story. Each picture is like a chapter in a book, which can do more than record the facts. 72 . Jacob Riis was among the first photojournalists, 73 Riis believed that poverty caused crime and he used photos to help him prove his point. A few years later , the photos of small children working in factories by Lewis Hine shocked the public .Hine’s pictures helped bring about laws to protect such children. 74 It takes science to have the photo come out clearly and art to make a photo that has a good design and expresses feeling. Photojournalists make an actual record of what they see. A photo, however , can be both a work of art and an actual record. It can record an important event as a beautiful or exciting picture. As historical and artistic documents(文献), photos can become more important over time . Today photojournalists still have their pictures appear in newspapers and magazines.75.
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