易发生缺血性坏死的骨折是（）。 A.骨盆骨折 B.肱骨髁上骨折 C.股骨颈骨折 D.

成熟T、B细胞定居的场所（）

A.骨髓

B.胸腺

C.淋巴结

D.脾

E.黏膜相关淋巴结组织

“登门槛”效应是指在提出一个较大要求之前，先提出一个小的要求，从而使别人接受较大要求的可能性增大的现象。
根据上述定义，下列各项中符合“登门槛”效应的是( )。

A．一项调查显示，某城市居民愿意为挽救濒危物种捐款的比例为48%，而如果先请人们在挽救濒危物种请愿书签名(几乎每个人都会同意签名)，再请他们捐款，愿意捐款的人数增加了20%
B．精明的商家在销售商品时往往把价格订得远远超过实际应有的价格，然后让顾客在讨价还价时接受一个相对的低价，实际上这个低价仍然高于商品应有的价格，但顾客往往乐此不疲
C．某品牌的一款笔记本电脑因性价比不高而市场占有率较低，厂家为此制定了个促销方案，购买该款笔记本电脑即赠送鼠标、mp3和U盘，结果该款笔记本电脑的销售量大幅度提高
D．某企业成功研制了一种祛除烟渍的洁白牙膏，由于其祛除烟渍效果较好而获得了市场的好评，该企业趁热打铁，又推出几款不同口感的洁白牙膏，尽管只是将前一种产品稍加改良而成，但仍然成为畅销产品

漏电保护装置用于（）。

A.防止人身触电事故

B.防止供电中断

C.减少线路损耗

D.防止漏电火灾事故

In the current immigration wave, something markedly different is happening here in the middle of the great American "melting pot." (46) There is a sense that, especially as immigrant populations reach a critical mass in many communities, it is no longer the melting pot that is transforming them, but they who are transforming American society.

American culture remains a powerful force—for better or worse—that influences people both here and around the world in countless ways. But several factors have combined in recent years to allow immigrants to resist, if they choose, the Americanization that had once been considered irresistible.

In fact, the very concept of assimilation is being called into question as never before. (47) Some sociologists argue that the melting pot often means little more than "Anglo conformity" and that assimilation is not always a positive experience—for either society or the immigrants themselves. And with today’s emphasis on diversity and ethnicity, it has become easier than ever for immigrants to avoid the melting pot entirely. Even the metaphor itself is changing, having fallen out of fashion completely with many immigration advocacy and ethnic groups. They prefer such terms as the "salad bowl" and the "mosaic," metaphors that convey more of a sense of separateness in describing this nation of immigrants.

(48) Among socially conservative families such as the Jacintos, who initially moved to California from their village in Mexico’s Guanajuato state, then migrated here in 1988 to find jobs in the meatpacking industry, bad influences are a constant concern. They see their children assimilating, but often to the worst aspects of American culture.

Their concerns reflect some of the complexities and ambivalence that mark the assimilation process these days. Immigrants such as the Jacintos are here to stay but remain wary of their adoptive country. According to sociologists, they are right to be concerned.

"If assimilation is a learning process, it involves learning good things and bad things," said Ruben G. Rumbaut, a sociology professor at Michigan State University. "It doesn’t always lead to something better."

The ambivalence of assimilation can cut both ways. Many native-born Americans also seem to harbor mixed feelings about the process. (49) As a nation, the United States increasingly promotes diversity, but there are underlying concerns that the more emphasis there is on the factors that set people apart, the more likely that society will end up divided.

With Hispanics, especially Mexicans, accounting for an increasing proportion of U.S. population growth, it is this group, more than any other, that is redefining the melting pot.

Hispanics now have overtaken blacks as the largest minority group in Nebraska and will become the biggest minority in the country within the next seven years, according to Census Bureau projections. (50) The nation’s 29 million Hispanics, the great majority of them from Mexico, have thus become the main focus for questions about how the United States today is assimilating immigrants, or how it is being transformed.

(49) As a nation, the United States increasingly promotes diversity, but there are underlying concerns that the more emphasis there is on the factors that set people apart, the more likely that society will end up divided.

根据土地用途土地可分为哪几类？