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往水样中投加一些化学试剂（保护剂）可固定水样中某些待测组分，经常使用的水样保护剂有各种（）、（）、和（）、加入量因需要而异。

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参考答案：酸；碱；生物抑制剂

单项选择题

单效蒸发中，原料液的温度越高，蒸发时的单位蒸汽消耗量（）。

A.越大

B.越小

C.不变

D.无法确定
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[A] Possible ways to keep free from Alzheimer’s
[B] Deficiency of data-collecting in the study
[C] The new findings of ineffectiveness of past cures
[D] Weak evidence of the research
[E] How the new analysis coming from
[F] Future direction of the research concerned
[G] Traditional beliefs in preventive measures

Lifestyle May Not Prevent Alzheimer’s


A comprehensive analysis by an independent government panel has found that there is not enough scientific evidence to date to support the advice doctors currently give—such as exercising, doing crossword puzzles or eating a Mediterranean-style diet—for preventing or controlling symptoms of Alzheimer’s disease and dementia.
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As rates of age-related dementia and Alzheimer’s disease have continued to rise in the U.S.—largely because Americans are living longer and the over-65 population has swelled to record highs—researchers have worked relentlessly to understand the causes of these mind- robbing diseases and to help prevent or slow their progression. To clarify the state of the current evidence and offer physicians clearer treatment guidelines, the National Institutes of Health (NIH) in early 2009 commissioned a detailed analysis of existing studies, covering 165 papers published between 1984 and 2009.
(42)______
For years, the prevailing hypothesis has been "Use it or lose it" when it comes to avoiding gradual age-related mental decline. Data has associated behaviors such as keeping the mind actively engaged throughout life, staying physically active, eating certain foods and supplementing the diet with specific vitamins and nutrients with lower rates of dementia in old age. These lifestyle factors appeared to limit cognitive decline of various kinds, from occasional "senior moments" to the more serious episodes of cognitive impairment that can be a prelude to Alzheimer’s disease.
(43)______
Now researchers at Duke University report in the current issue of the Annals of Internal Medicine that the data on the preventive effects of lifestyle factors is not as p as they had thought. Led by Brenda Plassman, a professor of psychiatry and behavioral sciences, the study authors analyzed decades’ worth of research, including observational studies in which scientists looked retrospectively at a group of participants to tease out associations between certain behaviors (like exercise) and selected effects (like scores on tests of memory and cognitive skills), as well as the more definitive clinical trials that randomly assign volunteers to intervention or control groups and then assess how the intervention affects cognitive ability.
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Overall, the researchers say they were dismayed with the paucity and weakness of the existing evidence. "When we applied rigorous but consistent standards to review all the studies, we found that there was not sufficient evidence to recommend any single activity or factor that was protective of cognitive decline later in life, " says Plassman.
(45)______
However weakly, though, the review did support what doctors know about risk factors for cognitive decline: smoking, diabetes, depression, metabolic syndrome and specific gene variants were all linked with increased risk of developing Alzheimer’s disease. In addition, preventive behaviors such as eating a Mediterranean diet, exercising, maintaining cognitive engagement (doing puzzles, learning new things) and fostering extensive social relationships were linked to a lower risk.
The problem is that none of these relationships were particularly robust, the authors say. And none were p enough to justify recommending the behaviors to people who want to prevent or slow down the onset of dementia. The findings led the NIH to issue Monday’s state-of-the-science statement, in which the agency notes, "Currently, firm conclusions cannot be drawn about the association of any modifiable risk factor with cognitive decline or Alzheimer’s disease." Although the statement does not constitute an official policy or government recommendation, it serves as a guideline for doctors advising patients about the best evidence on the role of lifestyle factors in Alzheimer’s prevention.
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