D Holding a cell phone against your ear or storing it in your pocket may be dangerous to your health. This explains a warning that cell phone manufacturers include in the small print that is often ignored when a new phone is purchased. Apple, for example, doesn’t want iPhones to come closer to you than 1.5 centimeters; Research In Motion, BlackBerry’s manufacturer, recommends 2.5 centimeters. If health issues arise from cell phone use, the possible effects are huge. Voice calls - Americans chat on cell phones 2.26 trillion(万亿)minutes annually - earn $109 billion for the wireless carriers. Devra Davis, an expert who has worked for the University of Pittsburgh, has published a book about cell phone radiation, “Disconnect.” The book surveys scientific research and concludes the question is not settled. Brain cancer is a concern that Ms. Davis examines. Over all, there has not been an increase in its incidence since cell phones arrived. But the average masks an increase in brain cancer in the 20-to-29 age group and a drop for the older population. “Most cancers have multiple causes,” she says, but she points to laboratory research that suggests low-energy radiation could damage cells that could possibly lead to cancer. Children are more vulnerable to radiation than adults, Ms. Davis and other scientists point out. Radiation that penetrates only five centimeters into the brain of an adult will reach much deeper into the brains of children because their skulls are thinner and their brains contain more absorptive fluid（易吸收的液体）. No studies have yet been completed on cell phone radiation and children, she says. Henry Lai, a research professor in the bioengineering department at the University of Washington, began laboratory radiation studies in 1980 and found that rats exposed to radiation had damaged DNA in their brains. Ms. Davis recommends using wired headsets or the phone’s speaker. Children should text rather than call, she said, and pregnant women should keep phones away from the abdomen（腹部）. 小题1:Why is the warning in the small print?
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