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问题 选择题

将适量CO2气体通入下列溶液中，不会析出沉淀或晶体的是（　　）

A．饱和Na2CO3溶液

B．CaCl2溶液

C．Na2SiO3溶液

D．Ca（ClO）2溶液

答案

A、由于碳酸钠的溶解度大于碳酸氢钠的溶解度，向饱和碳酸钠溶液中通入二氧化碳，反应生成了溶解度较小的碳酸氢钠，会有晶体析出，故A错误；

B、氯化钙溶液不与二氧化碳发生反应，不会析出沉淀，故B正确；

C、硅酸钠溶液中通入二氧化碳会生成硅酸沉淀，故C错误；

D、次氯酸根离子溶液中通入少量的二氧化碳，反应生成了碳酸钙沉淀，故D错误；

故选B．

单项选择题

True, some of the attacks against whites by blacks are for money and valuables. But, others ale revenge assaults by blacks for a real or imagined racial insult. It is equally true that the vast majority of violent crimes against whites are committed by whites, while the vast majority of violent crimes against blacks are committed by other blacks. Yet even after discounting crimes that are hastily and erroneously (错误地，不正确地) tagged as racially motivated, many blacks do attack whites because they all white. A 1998 Justice Department study confirmed that nearly 20% of the more than 4,000 hate crimes well committed against whites, and their attackers were blacks. The Southern Poverty Law Center also notes that there is a huge escalation in black-on- white violence from nearly none at the beginning of the 1990s.

A collection of white supermacists and rightist extremist groups have eagerly made black-on- white violence a wedge issue in their movement to paint blacks as the prime racial hate mongers in America. The New Century Foundation, an ultra-conservative think-tank, has launched a full- blown national campaign to alert whites to the danger of black hate crimes. These groups and individuals magnify hate crimes by blacks in order to back their social agenda. They oppose affirmative action programs and per hate crime laws. They downplay, or justify, the proliferation of white-supremacist-tinged paramilitary groups, police violence, and racial profiling. And they lobby hard for more prisons, police, and tougher laws.

Black-on-white violence also reinforces white fears of blacks as the ultimate menace to society. When blacks say or do nothing about these attacks, it is taken by some as a tacit signal that blacks put less value on white lives than black lives. This is a terrible price for black silence on hate crimes committed by blacks.

The phrase "hate crime" (Line 4, Paragraph 2) refers to the crime motivated by ().

A. the hate for enemy

B. racial hate

C. the hate for homoerotism (同性恋)

D. the hate for the rich
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单项选择题 A1/A2型题

下列哪一项不属于常用盖髓剂的性质要求（）。

A.能促进牙髓组织修复再生

B.对牙髓组织具有较好的生物相容性

C.有较强的杀菌或抑菌作用

D.有较强的渗透作用

E.药效稳定但可不持久
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