听力原文：Italian scientists have raised new health concerns about the safety of using mobile phones, with research showing radio waves from the handsets makes cancerous cells grow more aggressively. When Fiorenzo Marinelli and his colleagues at the National Research Council in Bologna exposed leukemia cells in the laboratory to 48 hours of continuous radio waves they initially killed the cancer cells but then made the surviving tumor cells replicate more rapidly.
We don't know what the effects would be on healthy human cells, Marinelli told New Scientist magazine. In the Italian study, after 24 hours 20 percent more leukemia cells died than healthy cells but longer exposure to the radio waves triggered genes in the surviving cancer cells to divide aggressively.
The results of the study do not show any direct threat to human health but they support the belief of some scientists who say radiation can damage DNA and destroy the cell repair system, thus making tumors more deadly. But animal studies, including recent research by Australian scientists at the Institute of Medical and Veterinary Science in Adelaide, have shown that radiation from mobile phones does not trigger the growth of tumors.
The WHO (i.e., The World Health Organization) has called for more research into the potential health hazards of mobile phones and has urged people to limit their use of them. A British government inquiry, which concluded that there was no evidence that mobile phones are a danger to health, has advised parents to discourage their children, whose brains are still developing, from using them excessively.
What is the speaker's main topic？
A．Effects of using mobile phones on healthy human cells.
B．Risks of developing cancer involved in the use of mobile phones.
C．Damage to healthy cells caused by the use of mobile phones.
D．The potential health hazards of mobile phones on humans.
Cancer is used generically for more than 100 different diseases, including malignant tumors of different sites such as breast, stomach, colon, lung and mouth.【1】The disease arises principally as a consequence of individual exposure to the substances that cause cancer in what individuals inhale, eat and drink, or are exposed to in their personal or work environment. Personal habits, such as tobacco use, dietary and physical activity patterns—well as occupational and environmental conditions—rather than genetic factors, play the major roles in the development of cancer.
Many of the chronic diseases risk and the diseases themselves overlap. In developed countries, cancer is the second-biggest cause of death after cardiovascular disease (CVD), and epidemiological evidence points to this trend emerging in the less developed world. This is particularly true in countries of "transition" or middle income countries such as in South America and Asia. Already more than half of all cancer cases occur in developing countries.
There are approximately 20 million people living with cancer at the moment; by 2020 there will an estimated 30 million. And the impact is far greater than the number of cases alone would suggest.【2】Regardless of prognosis, the initial diagnosis is of- ten perceived by patients as life-threatening, with over one-third of sufferers experiencing clinical anxiety and depression. Cancer can also be profoundly distressing as well as economically disruptive to patients' families. The clinical care of cancer patients is a costly element in public health budgets.
【3】Dietary factors are estimated to account for approximately 30% of cancers in Western countries, making diet second only to tobacco as a preventable cause of cancer. This proportion is thought to be about 20% in developing countries and is projected to grow. As developing countries become urbanized, patterns of cancer, particularly those most strongly associated with diet and physical activity, tend to shift towards the patterns of economically developed countries. Cancer rates also change as populations move between countries and adopt different dietary patterns.
The relative importance of cancers as a cause of death is increasing. The incidence of lung cancer and cancers of the colon and breast generally increases in parallel with economic development, as stomach cancer declines. Cancer is also strongly associated with social and economic status. Cancer risk factors are highest in groups with the least education. In addition, patients in the lower socioeconomic classes have consistently poorer survival rates than those in higher social class.
In recent years, substantial evidence has pointed to the link from overweight and obesity, to many types of cancer such as breast and kidney.【4】The composition of the diet is also important since fruit and vegetables may have a protective effect by decreasing the risk for some cancer types such as oral and gastric cancer.
Regular physical activity has also been seen to have a protective effect in reducing the risk of breast cancer. High intake of preserved meat or red meat might be associated with increased risk of colorectal cancer. Another aspect of diet clearly related to cancer risk is the high consumption of alcoholic beverages, which convincingly increase the risk of oral cavity, liver and breast cancers.
The wealth of knowledge that already exists about cancer risk factors provides obvious and ample scope for action to reduce the cancer burden of all countries. After tobacco, overweight and obesity seems to be the most important avoidable cause of cancer.
【5】Given that poor nutrition, physical inactivity, obesity tobacco and alcohol are risk factors common to other chronic diseases such as CVD, type 2 diabetes, and respiratory diseases, conducting a cancer prevention program withi
Since the early 1980s, scientists have revealed some 40 human genes involved in cancer. These genes are essential for normal growth, but can be subverted to cause a tumor.
Dr. Jorge Yunis of the University of Minnesota Medical School in Minneapolis has found that 70 percent of oncogenes, or cancer-causing genes, are located near inherited weak points on chromosomes(染色体). Varying from individual to individual, vulnerable to chemical carcinogens(致癌剂), X rays and other cancer-inducing agents.
"If a chromosome snaps apart in the immediate vicinity of an oncogene," says Yunis, "normal genetic control mechanisms could break down and the stage would be set for the formation of cancer." Younis has shown that such a sequence occurs at the beginning of numerous leukemias (白血病), lymphomas(淋巴瘤) and some tumors of the lung, colon(结肠) and breast.
Yunis and other investigators have found that petroleum-based products--notably pesticides and insecticides-damage specific sites on at least two of the 23 pairs of human chromosomes that carry genetic information. Similarly, tobacco smoke tends to attack a part of another chromosome.
From paragraph 1, we know that some 40 genes involving in cancer are ______. ()
A．harmful to the human body
B．necessary to the human body
C．the elements that form. cancer
D．useless to the human body
