问题 选择题

关于密度,下列说法正确的是(  )

A.物质的质量越大,其密度也越大

B.由密度公式可知,密度与物体的质量成正比,与物体的体积成反比

C.空气也有密度,而且空气密度的数值在任何情况下都不会改变

D.铁的密度与它的温度、状态有关

答案

A、密度是物质的一种特性,不随物体的质量、体积的变化而变化.此选项错误;

B、密度计算公式ρ=

m
V
只是定义式,对于同种物质来说,密度是定值,与质量、体积无关.此选项错误;

C、空气也有密度,但空气密度的数值随着空气的状态、温度的变化而变化.此选项错误;

D、一定质量的物质,温度升高体积膨胀,所以密度减小;同种物质,状态不同密度不同.所以铁的密度与温度和状态都有关系.此选项正确.

故选D.

填空题
单项选择题

Text 1

Mary Eberstadt writes in Home-Alone America that growing obesity, the high incidence of sexually transmitted disease among teenagers and an overdependence on drugs such as Ritalin for attention deficit disorder are often the fault of parents who "outsource" their responsibilities.

"We tend to think that the problems with juveniles are located at the bottom end of the social spectrum, but latchkey children are more common among the affluent," said Eberstadt, a mother of four who is a conservative writer and research fellow at Stanford University’s Hoover Institution.

According to the most recent figures from the US Census Bureau, 41% of children aged 12 to 14 regularly look after themselves at the end of the school day. The figures rise with prosperity. For children aged 5 to 14, "self-care increases from 11% of children in poverty to 22% of those with family incomes at least double the poverty line."

Eberstadt’s book is dividing sociologists, critics and partisans in the "mommy wars" between stay-at-home and working parents. A child clings to the ankles of his smartly dressed mother to stop her leaving for work on the front of the book; he does the same to his father on the back.

P. J. O’Rourke, the conservative commentator and satirist, supports Eberstadt’s thesis. "If you don’t think (her) arguments have merit, try treating your dog the way America treats its kids," he said.

"Give the puppy her own set of house keys and put her in front of the television instead of taking her for a walk. Let her eat anything she wants and house train herself. Send her to another master for visitation at the weekends. And when she comes into heat, turn her loose in the pound."

James Q. Wilson, author of The Marriage Problem: How Our Culture Has Weakened Families is one of the intellectual forces behind zero tolerance policing. He praised the book’s "great, unarguable theme that parental care is of decisive importance in shaping the character of our children".

Feminist critics, in contrast, accuse Eberstadt of Taliban-style thinking. The Washington Post attacked her "seductive" but "nasty" opinions and lack of "interest in how real people live or think about their lives".

Eberstadt insists that she is not ordering women back to the home. "The bottom line is a lot more nuanced," she said. "It doesn’t have to be ’you’ there after school, but there are not enough protective, supporting, loving adults around."

Neighbourhoods, she added, "are so emptied of adult presence that even the richest kids just go home, throw the deadbolt and get no exercise more strenuous than walking from the video game to the refrigerator." The result of being home alone is not just snacking and obesity but casual sex, leading to an explosion in venereal diseases that can lead to infertility and cervical cancer, Eberstadt said.

Mary Eberstadt would mostly agree()

A.the problems with juveniles are located at the bottem end of the social spectrum.

B.women shall not go out to work but stay at home.

C.children in rich families are lack of exercises.

D.leaving children alone will lead to many diseases.