You're in a department store and you see a couple of attractive young women looking at a sweater．You listen to their conversation：

    “I can't believe it－Lorenzo Bertolla! They are almost impossible to find．Isn't it beautiful? And it's a lot cheaper than the one Sara bought in Rome．”

    They leave and you go over to see this incredible sweater．It's nice and the price is right．You've never heard of Lorenzo Bertolla, but those girls looked really stylish．They must know．So, you buy it．You never realize that those young women are employees of an advertising agency．They are actually paid to go from store to store, talking loudly about Lorenzo Bertolla clothes．

    Every day we notice what people are wearing, driving and eating．If the person looks cool, the product seems cool, too．This is the secret of undercover marketing．Companies from Ford to Nike are starting to use it．

    Undercover marketing is important because it reaches people that don't pay attention to traditional advertising．This is particularly true of the MTV generation－consumers between the age of 18 and （3）It's a golden group．They have a lot of money to spend, but they don't trust ads．

    So advertising agencies hire young actors to “perform” in bars and other places where young adults go．Some people might call this practice misleading, but marketing executive Jonathan Ressler calls it creative．“Look at traditional advertising．Its effectiveness is decreasing．”It is true, because everyone knows an ad is trying to persuade you to buy something．However, you don't know when a conversation you overhear is just a performance．

三衢道中

（宋代）曾几

梅子黄时日日晴，小溪泛尽却山行。

绿阴不减来时路，添得黄鹂四五声。

25℃时,将稀氨水逐滴加入稀盐酸中，当溶液的pH＝7时，下列关系不正确的是（     ）

萤火虫

尹衍国

    ①“萤火虫，萤火虫，飞到西，飞到东。好像星星眨眼睛，好像盏盏小灯茏……”

    ②关于萤火虫，有很多有趣的故事。相传，我国晋朝时有个青年叫车胤，他酷爱学习，但由于家贫买不起蜡烛，不能读书，于是就捉了很多萤火虫，装在薄薄的布袋子里。四五十只萤火虫发出的光；真能抵得上一支点燃的蜡烛呢!他就借着萤火虫的光刻苦学习，后来成为一位有大学问的人。

    ③萤火虫的一生要变四个模样。萤火虫妈妈喜欢在潮湿腐烂的草丛中产卵，它的卵小得很，要用放大镜才能看得见。卵孵化出幼虫后，生活几天就变成蛹。最后由蛹变成萤火虫。萤火虫的幼虫个儿很小，但胆量很大，敢与蜗牛较量，直至把蜗牛吃掉。萤火虫幼虫有一套神奇的“法宝”。你看，当幼虫找到蜗牛以后，先用它那针头一样的嘴巴在蜗牛身上敲几下，这是干什么呢?原来这是给蜗牛打麻醉针。连打几下以后，蜗牛就迷迷糊糊地失去了知觉，动弹不得，最后终于瘫痪了。这时候，幼虫又狠狠地给蜗牛注射消化液。蜗牛皮内的肉开始化成了稀稀的鲜美的肉汁。这时幼虫便呼唤它的同伴们，兴高采烈地围在蜗牛四周，一齐把针管般的嘴巴插进蜗牛的皮内，津津有味地吸起来。幼虫们吸足了，蜗牛也就完了。它们帮农民除了害，立了功，是农作物的好朋友。

    ④幼虫长到成虫以后，开始在夜空中飞舞，一边飞舞一边发出短暂的闪光。萤火虫闪光是为了什么呢?原来是在招引异性。那雄萤火虫在地面上空飞舞时发出闪光，意思是在寻问：“萤姑娘，你在哪里?”附近草地上的雌萤火虫也发出闪光，那是回答的信号，意思是说：“萤小伙，我在这里。”雄萤火虫得到信号以后，便向雌萤火虫飞去，直到甜蜜地相会为止。

    ⑤萤火虫那美丽的闪光是怎么发出来的呢?科学家们经过仔细观察研究，发现在萤火虫的腹部有个发光器。这发光器由发光层、反射层和透明表皮三个部分组成。发出的光是由呼吸时使称为“荧光素”的发光物质氧化所致。萤火虫发出的光是冷光，它不会产生热。人们通过萤火虫的发光原理发明了荧光灯——日光灯，它比同样功率的普通灯泡明亮得多。后来人们又发明了矿灯，用在矿井里。因为矿井里有瓦斯，达到一定浓度，遇到一定热量就会爆炸，这种灯不发热，所以使用安全。科学家们还用荧光素和荧光素酶制成生物探测器，把它发射到其它星球表面，去探测那里是否有生命存在。

    ⑥你瞧，小小的萤火虫，趣闻还真不少呢！