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：连词辨析题。空格后为seemingly意为“看上去”， 前半句表示“表面上看起来没有什么伤害”，再根据后文语意“精神不集中可能会对我们的职业、社交和个人带来影响”，由此可知前半句和后半句是转折关系。故本空应填入While，表示转折。句子大意为：虽然表面看上去无害，但会对我们产生影响。

错项排除：A项的If、B项的Unless以及C项的Once均用于表示句子前后的条件关系，引导条件状语从句，不能表示转折，故排除。