题目内容
EFFECTS OF IONIZING RADIATION 1 Everyone on Earth is continually exposed to small, relatively harmless amounts of ionizing radiation, known as background radiation, from natural sources such as soil and rock. However, other types of ionizing radiation--x-rays, ultraviolet radiation from the sun, and alpha, beta, and gamma radiation emitted by radioactive isotopes--have the potential to harm the human body. Ionizing radiation has enough energy to remove one or more electrons from the atoms it hits to form positively charged ions that can react with and damage living tissue. Most damage occurs in tissues with rapidly dividing cells, such as the bone marrow, where blood cells are made, and the digestive tract, whose lining must be constantly renewed. 2 Exposure to ionizing radiation can damage cells in two ways. The first is genetic damage, which alters genes and chromosomes. This can show up as a genetic defect in children or in later generations. The second type of damage is somatic, which causes victims direct harm in the form of bums, miscarriages, eye cataracts, some types of leukemia, or cancers of the bone, thyroid, breast, skin, and lung. Small doses of ionizing radiation over a long period of time cause less damage than the same total dosage given all at once. Exposure to a large dose of ionizing radiation over a short time can be fatal within a few minutes to a few months later. What types of tissues are harmed most by ionizing radiation
查看答案
搜索结果不匹配？点我反馈
更多问题
THE ROLE OF GOVERNMENT IN THE ECONOMY 1 Because most people do not volunteer to pay taxes or police their own financial affairs, governments cannot influence economic activity simply by asking people to pollute less, to give money to the poor, or to be innovative. To accomplish these things, governments have to pass laws. Since the early twentieth century, governments of countries with advanced industrial or service economies have been playing an increasing role in economics. This can be seen in the growth of government taxation and spending, in the growing share of national income devoted to income-support payments, and by the enormous increase in the control of economic activity. 2 The large-scale organization of business, as seen in mass production and distribution, has led to the formation of large-scale organizations--corporations, labor unions, and government structures--that have grown in importance in the past several decades. Their presence and growing dominance have shifted capitalist economies away from traditional market forces and toward government administration of markets. 3 In the United States, government provides a framework of laws for the conduct of economic activity that attempt to make it serve the public interest. For instance, the individual states and the federal government have passed laws to shield investors against fraud. These laws specify what information has to be disclosed to prospective investors when shares of stocks or bonds are offered for sale. Another important area of law concerns the labor force, such as regulation of work hours, minimum wages, health and safety conditions, child labor, and the rights of workers to form unions, to strike, to demonstrate peacefully, and to bargain collectively through representatives of their own choosing. 4 In other nations, the ways in which governments intervene in their economies have varied; however, governments everywhere deal with essentially the same issues and participate in economic activity. Even governments that are reluctant to regulate commerce directly have undertaken large-scale projects such as hydroelectric and nuclear energy developments, transportation networks, or expansion of health, education, and other public services. All of the following are given as issues concerning the labor force EXCEPT
EFFECTS OF IONIZING RADIATION 1 Everyone on Earth is continually exposed to small, relatively harmless amounts of ionizing radiation, known as background radiation, from natural sources such as soil and rock. However, other types of ionizing radiation--x-rays, ultraviolet radiation from the sun, and alpha, beta, and gamma radiation emitted by radioactive isotopes--have the potential to harm the human body. Ionizing radiation has enough energy to remove one or more electrons from the atoms it hits to form positively charged ions that can react with and damage living tissue. Most damage occurs in tissues with rapidly dividing cells, such as the bone marrow, where blood cells are made, and the digestive tract, whose lining must be constantly renewed. 2 Exposure to ionizing radiation can damage cells in two ways. The first is genetic damage, which alters genes and chromosomes. This can show up as a genetic defect in children or in later generations. The second type of damage is somatic, which causes victims direct harm in the form of bums, miscarriages, eye cataracts, some types of leukemia, or cancers of the bone, thyroid, breast, skin, and lung. Small doses of ionizing radiation over a long period of time cause less damage than the same total dosage given all at once. Exposure to a large dose of ionizing radiation over a short time can be fatal within a few minutes to a few months later. All of the following are examples of somatic damage EXCEPT
ICE 1 Two conditions are necessary for the formation of ice: the presence of water and temperatures below freezing. Ice in the atmosphere and on the ground can assume various forms, depending on the conditions under which water is converted to its solid state~ Ice that forms in the atmosphere can fall to the ground as snow, sleet, or hail. Snow is an assemblage of ice crystals in the form of flakes; sleet is a collection of frozen raindrops, which are actually ice pellets. Hail consists of rounded or jagged lumps of ice, often in layers like the intemal structure of an onion. Ice also forms directly on the ground or on bodies of water. In North America, ice forms in late autumn, winter, and early spring. On very large bodies of water, it may not form until late winter because there must be several months of low temperatures to chill such large amounts of water. 2 On puddles and small ponds, ice first freezes in a thin layer with definite crystal structure that becomes less apparent as the ice thickens. On lakes large enough to have waves, such as the Great Lakes, the first ice to form is a thin surface layer of slush, sometimes called grease ice, which eventually grows into small floes of pancake ice. If the lake is small enough or the weather cold enough, the floes may freeze together into a fairly solid sheet of pack ice. Pack ice may cover the entire lake or be restricted to areas near the shore. 3 Because water expands when it freezes, ice is less dense than liquid water and therefore floats rather than sinks in water. As ice floats on the surface of a lake, ocean, or river, it acts as an insulator and is thus important in maintaining the balance of the ecosystem. Without the insulating effect of floating ice sheets, surface water would lose heat more rapidly, and large bodies of water such as the Arctic Ocean and Hudson Bay might freeze up completely. In paragraph 1, the author makes the point that
He managed to ______ us of the truth of the news.
微信支付 
支付宝支付