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。空格前为动词remember，remember后接宾语从句，空格处应填入宾语从句的引导词。结合上下文语意，文章开头指出许多人到中年会发现自己的记忆力不如以前了。我们会突然想不起刚刚把钥匙放在________，很明显此处应该是“忘记把钥匙放在了哪里”，故本空应填入where，表示地点。

错项排除：原句中已有a moment ago作为时间状语，B项when与此重复，故排除。C项that在引导宾语从句时不充当任何成分，但原句缺少地点状语，故C项错误。D项why表示原因，和上下文语意不符，故排除。