问题 单项选择题

后牙铸造金属全冠牙体预备时,以下选项正确的是().

A.为保存更多的余留牙体组织,面磨除不能超出1mm

B.面预备形成一个平面

C.轴面预备必须无倒凹,无聚合度,并与牙长轴平行,以保证修复体有足够的固位力

D.面功能尖斜面应预备出不少于1.5mm的空间

E.轴面边缘预备形成1mm的无角肩台

答案

参考答案:D

解析:

铸造金属全冠的面牙体预备时,功能尖斜面即功能尖的工作斜面要求预备出不少于1.5mm的修复空间,以保证铸造金属全冠在该部位有足够的修复材料厚度,从而保证修复体足够的抗力形和耐用性。

单项选择题

Some people talk about immigration in terms of politics, some in terms of history. But the core of the matter is numbers. The Labor Department says that immigrants make up about 15 percent of the work force. It’s estimated that a third of those are undocumented workers. The Pew Hispanic Center estimates that one in four farmhands in the United States is an undocumented immigrant, and that they make up a significant portion of the people who build our houses, clean our office buildings and prepare our food.

America has become a nation dependent on the presence of newcomers, both those with green cards and those without. Business leaders say agriculture, construction, meatpacking and other industries would collapse without them.

Sure, it would be great if everyone were here legally, if the immigration service weren’t such a disaster that getting a green card is a life’s work. It would be great if other nations had economies robust enough to support their citizens so leaving home wasn’t the only answer. But at a certain point public policy means dealing not only with how things ought to be but with how they are. Here’s how they are: these people work the jobs we don’t want, sometimes two and three jobs at a time. They do it on the cheap, which is tough, so that their children won’t have to, which is good. They use services like hospitals and schools, which is a drain on public coffers, and they pay taxes, which contribute to them.

Immigration is never about today, always about tomorrow, an exercise in that thing some native-born Americans seem to have lost the knack for: deferred gratification. It’s the educated man who arrived in the Washington D. C., area and took a job doing landscaping, then found work as a painter, then was hired to fix up an entire apartment complex by someone who liked his work ethic. He started his own business and wound up employing others. Does it matter that he arrived in this country with no work visa if he is now supporting the nation’s economy

If any towns, whose aging populations were on the wane before the immigrants arrived, succeed in driving newcomers away, those who remain will find themselves surrounded by empty storefronts, deserted restaurants and houses that will not sell. It’s the civic equivalent of starving to death because you don’t care for the food. But at least everyone involved can tell themselves their town wasted away while they were speaking English.

In the author’s opinion, why do undocumented immigrants straggle for life()

A. provide services to US citizens

B. do those the US citizens don’t want to do

C. enable their own country be robust enough to support themselves

D. make their children to be legal citizens of the US

名词解释