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decaying radon (氡) atoms can destroy the living cells they strike and increase
the likelihood that those cells will later become cancerous. Researchers have
now directly demonstrated that neighboring cells not suffering direct hits can
be harmed, too. They've also taken a step toward showing how this type of
radiation, called alpha particles, indirectly hurts those bystanders.
Radon derives from the decay of uranium (铀) and seeps naturally into the
air from the ground. It's the primary environmental source of alpha particles,
which contribute to cancer risk by causing aberrations (失常) in DNA. Alpha
particles from inhaled radon are second only to smoking as a cause of lung
cancer. Because a person's exposure to alpha particles
typically is low, researchers have had to estimate public health threats from
radon by guess from the effects of higher doses of alpha radiation. Such data
comes primarily from studies of survivors of the atomic bombs that destroyed
Hiroshima and Nagasaki in Japan. The customary extrapolation (推测) assumes that
cancer risk is proportional to the dose of radiation even at low
doses. Radiation's effects in cell structure don't necessarily
reflect what happens in "a whole organism, with its full range of defense repair
mechanisms," says Duport. Processes such as DNA repair and cell death triggered
by radiation damage could cancel the effect on by stander cells observed in the
lab, he suggests. Furthermore, while a bystander effect can
contribute to cancer, other cell-to-cell interactions in living tissue "may
relieve increased risk." says Barry Michael, a radiation biophysicist at the
Gray Cancer Institute in Northwood, England. One of these interactions halts
cell division and hence cancer. "The jury is still out on whether cell-to-cell
effects lead to a greater or lower risk," Michael says.
单选题
The passage's main topic is ______.
A. The experiment done by researchers
B. Uranium is the key killer of neighboring cells
C. Cell-to-cell interaction can make up for the hurt cells
D. Bystander cells can be indirectly damaged by alpha particles
【答案解析】[解析] 根据第一段最后一句“They've also taken a step toward showing how this type of radiation, cared alpha particles, indirectly hurts those bystanders.”可知，研究者们也已经进一步证明这种叫做a粒子的辐射类型是如何间接地伤害那些局外人的，据此可知，此处说的辐射类型指代来自衰变的氡原子的辐射，所以B符合题意。
单选题
Which of the following is right for alpha particles?
A. They are the second killers to smoking as cause of lung cancer.
B. They can compensate for the abnormal DNA.
C. High dosage and low dosage of them have the same effect on people's
health.
A. By studying the data got from the survivors who had experienced atomic
radiation.
B. By carrying out the experiments in the lab.
C. By studying the features of the experiments.
D. By studying the features of the erperiments.
【正确答案】
A
【答案解析】[解析] 根据第三段内容“researchers have had to estimate public health threats from radon by guess from the effects of higher doses of alpha radiation. Such data comes primarily from studies of survivors of the atomic bombs that destroyed Hiroshima and Nagasaki in Japan.”可知，研究者们不得不通过猜测a粒子的高剂量来估计氡对公众健康的威胁，这些数据主要来自对遭受破坏日本广岛和长崎的原子弹的受害者的研究，所以选A。
单选题
From the passage, we can know the tone of the author is ______.