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．

山区常见的地质方面的自然灾害是____、____和____。

冼（xiǎn）星海在巴黎

    一九二九年，二十四岁的冼星海，因为参加学生运动，被学校开除了。他在远洋轮船上找了一个工作，就趁（chèn）这个机会到法国巴黎去，实现他学习音乐的愿望。

    在巴黎，冼星海的生活很艰难（nán）。他在饭店洗碗，在理发店扫地，还给别人看孩子、守电话、抄乐谱（pǔ），甚至拉着提琴到街头和咖啡店去卖艺（yì）。

    在那饥寒交迫的日子里，他好几次在楼梯上晕（yūn）倒，在马路上饿倒。但这都动摇不了他学习音乐的意志。

    后来，冼星海的音乐天才和苦学精神，得到了巴黎音乐家的赏识，他们给冼星海很多物质上的帮助和精神上的鼓励。冼星海终于考进了巴黎音乐高级作曲班。他是第一个考进这个班的东方人。

某研究小组为测定药物对体外培养细胞的毒性，准备对某种动物的肝肿瘤细胞（甲）和正常肝细胞（乙）进行动物细胞培养．下列叙述正确的是（　　）