As many people hit middle age, they often start to notice that their memory and mental clarity are not what they used to be. We suddenly can’t remember (1)_____ we put the keys just a moment ago, or an old acquaintance’s name, or the name of an old band we used to love. As the brain (2)_____, we refer to these occurrences as “senior moments.” (3)_____ seemingly innocent, this loss of mental focus can potentially have a(n) (4)_____ impact on our professional, social, and personal (5)_____.

     Neuroscientists, experts who study the nervous system, are increasingly showing that there’s actually a lot that can be done. It (6)_____ out that the brain needs exercise in much the same way our muscles do, and the right mental (7)_____ can significantly improve our basic cognitive (8)_____. Thinking is essentially a (9)_____ of making connections in the brain. To a certain extent, our ability to (10)_____ in making the connections that drive intelligence is inherited. (11)_____, because these connections are made through effort and practice, scientists believe that intelligence can expand and fluctuate (12)_____ mental effort.

     Now, a new Web-based company has taken it a step (13)_____ and developed the first “brain training program” designed to actually help people improve and regain their mental (14)_____.

     The Web-based program (15)_____ you to systematically improve your memory and attention skills. The program keeps (16)_____ of your progress and provides detailed feedback (17)_____ your performance and improvement. Most importantly, it (18)_____ modifies and enhances the games you play to (19)_____ on the strengths you are developing—much like a(n) (20)_____ exercise routine requires you to increase resistance and vary your muscle use.

答案精析：副词辨析题。本题需要理解上下文的逻辑关系。空格前的句子大意为“建立大脑联系的能力是与生俱来的”，空格后的句子大意为“建立联系需要通过努力和练习，因此科学家认为智力可以根据思维活动而增长或波动”。空格前后表示一种转折的关系，故本空应填入However。

错项排除：A项Therefore“因此”，表示因果关系，B项Moreover“而且”，表示递进关系，C项Otherwise“否则”表示条件关系，三项均不符合原文的逻辑关系，故排除。