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.（14）选？
上下文语义衔接+名词辨析前文提到脑力的下降导致人们会忘记很多事情，这说明脑力变得迟钝，现在有公司开发了一套程序帮助人们提高脑力，因此这里说的是提高脑力的敏锐度，和前面的迟钝性形成对比，因此只有选项C正确。选项A和B从意义上都说不通，选项D如果和mental放到一起，意思是处事和思考问题的灵活性，而不是指正常生理状态的脑力，它无法和脑力的生理衰老形成对比。因此，正确答案是C。
