Chronic insomnia is a major public health problem. And too many people are using     1    therapies, even while there are a few treatments that do work. Millions of Americans     2    awake at night counting sheep or have a stiff drink or     3    an pill, hoping it will make them sleepy.     4    experts agree all that self-medicating is a bad idea, and the causes of chronic insomnia remain     5    .
    Almost a third of adults have trouble sleeping, and about 10 percent have     6    of daytime impairment that signal true insomnia. But     7    the complaints, scientists know surprisingly little about what causes chronic insomnia, its health consequences and how best to treat it, a panel of specialists     8    together by the National Institutes of Health concluded Wednesday. The panel called     9    a broad range of research into insomnia,     10    that if scientists understood its     11    causes, they could develop better treatments.
    Most, but not all, insomnia is thought to     12    other health problems, from arthritis and depression to cardiovascular disease. The question often is whether the insomnia came first or was a result of the other diseases and how trouble sleeping in     13    complicates those other problems. Other diseases     14    , the risk of insomnia seems to increase with age and to be more     15    among women, especially after their 50s. Smoking, caffeine and numerous     16    drugs also affect sleep.
    The NIH is spending about $200 million this year on sleep-related research, some     17    to specific disorders and others     18    the underlying scientific laws that control the nervous system of sleep. The agency was     19    the pane's review before deciding what additional work should be     20    at insomnia. 
 
【正确答案】 A
【答案解析】 考查形容词辨析。此空所在句子意为:太多人正使用______的治疗方法,尽管有些方法确实是有效的。根据句意,此处应选A.unproven“未经验证的”。unknown“未知的”,improper“不恰当的”,imperative“必要的,不可避免的”,均不符合题意。