若多项式a²+kab+4b²是完全平方式，则常数k的值为（   ）．

    Open work spaces definitely have their benefits，but they come with the drawback of offering employees little to no control over visual distractions(干扰)．With so many people around and so much going on，some of us can easily get disturbed by this information overload and lose focus in what's really important．That's where the Focus Cap comes into play．

    “As we are still cavemen or mammals kept in an unnatural environment，I believe that only by reclaiming(收回)the normal，stress-free human state through simple tools and techniques can we finally release our actual creative potential and create our meaningful work for a brighter future，”says German designer Hannes Greblin，inventor of the Focus Cap．

    After looking at other products designed at minimizing visual distractions，Greblin decided that most of them were either too expensive or too uncomfortable to become mainstream，so he decided to go with something much simpler —a simple cap with a retractable visor(可伸缩的帽沿)．

    Greblin's Focus Cap is really straightforward．You just wear it like a regular cap'with the sides of the visor retracted，and just collapse the sides whenever you need to focus on what's ahead of you．Whether you're trying to focus on a task in an open work office．Trying to study at university，or practicing yoga in a park and trying to ignore stares from strangers，the Focus Cap can help．

    To be honest，this whole project sounds like a joke，but the Focus Cap does have its own website where people interested in this unusual accessory can actually sign up for updates on when it will go on sale．Greblin claims it will cost 30 euros($37)plus shipping．

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                                                                                                  爸爸教我读中国诗

                                                                                                               程怡

       ①十个月的时候，我得了一场可怕的脑膜炎，到了一岁半还不会说话，父母非常担心。一天，爸爸看报，我坐在他的膝上，指着某一个标题中的“上”字，爸爸说：“上？”我对他表示满意，赶紧从他的膝上爬下来，拽着他走到书箱前，得意洋洋地指着书箱外“函上”的“上”字，表明我认识这个字，这件事对父母而言，真是“上上大吉”！他们不再担心我有智力障碍了。之后，爸爸开始教我读诗。

       ②爸爸常教我念两个人的诗：一个是杜甫，一个是陆游。

       ③依稀记得，孩提时的一个夏夜，我困极了，趴在爸爸的膝上，爸爸摇着大蒲扇，满天的星斗朦朦胧胧的。“僵卧孤村不自哀，尚思为国戍轮台……”突然，爸爸那江西乡音很重的诵读声使我睁开了眼睛，我不知道那奇特的吟啸中有什么，但我一下子记住了这首诗。

       ④上学前我已经会背那首《示儿》：“死去元知万事空，但悲不见九州同。王师北定中原日，家祭无忘告乃翁。”爸爸问我懂不懂最后那句，我很得意地嚷嚷说：“那意思就是烧香磕头的时候别忘了告诉你爸爸！”当时，爸爸高兴得眼泪都流出来了。

       ⑤1959年秋，我上小学。那年冬天，爸妈因故很长时间不能住在家。姐姐是长女，照顾我和弟弟。一天晚上，爸爸出乎意料地出现在我们面前，令我们欢天喜地，难以入眠。躺在床上跟爸爸念杜甫的诗：“遥怜小儿女，未解忆长安。”爸爸问我懂不懂这诗句，我说：“我懂的，不过，爸爸想念我们的时候，我们也想念爸爸的。”爸爸不再说话，只是听我继续背他教我的诗。

       ⑥爸爸生命的最后几年，完全卧床不起。每当德沃夏克的大提琴协奏曲悲鸣的旋律在蕉影婆娑的窗边响起的时候，爸爸就会喃喃吟诵杜甫的诗。他告诉我，那一刻让他想起了故乡老宅，想起了祖母和母亲。

       ⑦那时我已在大学教中国古代文学，我理解父亲：人生无非家国之情，杜甫、陆游，我父亲他们这一代的知识分子，对家国，都有一种深情。父亲吟诗的声音，永远留在了我心底。

       ⑧很多年后，我看见报上某篇文章引了一首绝句，感觉就像遇到了一个老熟人。我没有念过那首诗，但我熟悉那种风格。回来一查，果然是陆游的诗，“征车已驾晨窗白，残烛依然伴客愁。”我当时的感受真是难以名状。爸爸在我童年时便种在我生命里的东西，突然宣告了它的无可移易的存在！