单选题如果a，b，c的算术平均值等于13，且，那么c=______．

单选题下列各组函数中，两个函数相同的是______A．B．f(x)=x，g(x)=C．f(x)=ln｜x｜，g(x)=lnxD．f(x)=1nx3，g(x)=3lnx

单选题若事件A发生必然导致事件B发生，则事件14和B的关系一定是()．

单选题等于______．

单选题设f(x)连续，则=______A.xf(x2)．B.-xf(x2)．C.2xf(x2)．D.-2xf(x2)．

单选题某商场举行周年让利活动，单件商品满300减180元，满200减100元，满100减40元；若不参加活动则打5.5折。小王买了价值360元、220元、150元的商品各一件，最少需要______。

单选题明朝负责复核驳正的机关是( ) A．大理寺 B．刑部 C．都察院 D．御史台

单选题Addiction is such a harmful behavior, in fact, that evolution should have long ago weeded it out of the population: if it's hard to drive safely under the influence, imagine trying to run from a saber-toothed tiger or catch a squirrel for lunch. And yet, says Dr. Nora Volkow, director of NIDA and a pioneer in the use of imaging to understand addiction, "the use of drugs has been recorded since the beginning of civilization. Humans in my view will always want to experiment with things to make them feel good. " That's because drugs of abuse co-opt the very brain functions that allowed our distant ancestors to survive in a hostile world. Our minds are programmed to pay extra attention to what neurologists call salience--that is, special relevance. Threats, for example, are highly salient, which is why we instinctively try to get away from them. But so are food and sex because they help the individual and the species survive. Drugs of abuse capitalize on this ready-made programming. When exposed to drugs, our memory systems, reward circuits, decision-making skills and conditioning kick in--salience in overdrive--to create an all consuming pattern of uncontrollable craving. "Some people have a genetic predisposition to addiction," says Volkow. "But because it involves these basic brain functions, everyone will become an addict if sufficiently exposed to drugs or alcohol. " That can go for nonchemical addictions as well. Behaviors, from gambling to shopping to sex, may start out as habits but slide into addictions. Sometimes there might be a behavior-specific root of the problem. Volkow's research group, for example, has shown that pathologically obese people who are compulsive eaters exhibit hyperactivity in the areas of the brain that process food stimuli--including the mouth, lips and tongue. For them, activating these regions is like opening the floodgates to the pleasure center. Almost anything deeply enjoyable can turn into an addiction, though. Of course, not everyone becomes an addict. That's because we have other, more analytical regions that can evaluate consequences and override mere pleasure seeking. Brain imaging is showing exactly how that happens. Paulus, for example, looked at drug addicts enrolled in a VA hospital's intensive four-week rehabilitation program. Those who were more likely to relapse in the first year after completing the program were also less able to complete tasks involving cognitive skills and less able to adjust to new rules quickly. This suggested that those patients might also be less adept at using analytical areas of the brain while performing decision-making tasks. Sure enough, brain scans showed that there were reduced levels of activation in the prefrontal cortex, where rational thought can override impulsive behavior. It's impossible to say if the drugs might have damaged these abilities in the relapsers--an effect rather than a cause of the chemical abuse--but the fact that the cognitive deficit existed in only some of the drug users suggests that there was something innate that was unique to them. To his surprise, Paulus found that 80% to 90% of the time, he could accurately predict who would relapse within a year simply by examining the scans. Another area of focus for researchers involves the brain's reward system, powered largely by the neurotransmitter dopamine. Investigators are looking specifically at the family of dopamine receptors that populate nerve cells and bind to the compound. The hope is that if you can reduce the effect Of the brain chemical that carries the pleasurable signal, you can loosen the drug's hold.

单选题社会主义道德建设的核心是______。 A．为人民服务 B．集体主义 C．诚实守信 D．爱国主义

单选题Onenumberwillbechosenrandomlyfromeachofthesetsabove.IfxrepresentsthechosenmemberofSetXandyrepresentsthechosenmemberofSetY,whatistheprobabilitythatwillbeaninteger?

单选题若事件{max(X，Y)=2}与事件{min(X，Y)=1}相互独立，则Cov(X，Y)=（）

单选题若f(-x)=-f(x)，且在(0，+∞)内f"(x)＞0，f"(x)＞0，则在(-∞，0)内______．

单选题 若方程组有解 则应为 A、 B、 C、 D、

单选题若关于x的不等式，|x-2|+|x+1|＜b的解集是，则b的取值范围是()．

单选题设向量β可由向量组α 1 ，α 2 ，…，α m 线性表示，但不能由向量组(Ⅰ)：α 1 ，α 2 ，…，α m-1 线性表示，记向量组(Ⅱ)：α 1 ，α 2 ，…，α m-1 ，β，则______

单选题______A．B．3xC．xD．3

单选题______A．∞B．0C．1D．

单选题 A、 B、 C、3 D、0

单选题点(-3，-1)关于直线3x+4y-12=0的对称点是( )．

单选题若，，则(       )