如图所示,放在水平地面上的物体a上叠放着物体b,a和b间用轻质弹簧相连,已知弹簧

题型:选择题

问题:

如图所示,放在水平地面上的物体a上叠放着物体bab间用轻质弹簧相连,已知弹簧处于压缩状态,整个装置处于静止状态,则关于ab的受力分析正确的是 ( )

A.b受到向右的摩擦力

B.a受到b对它的向右的摩擦力

C.地面对a的摩擦力向右

D.地面对a无摩擦力作用

考点:静摩擦力滑动摩擦力、动摩擦因数
题型:选择题

下列数据库技术的术语与关系模型的术语的对应关系中正确的足 ______。

A.记录与属性

B.字段与元组

C.记录类型与关系模式

D.实例与关系

题型:选择题

Most parents of kids under age 8 don't worry about how much time they spend watching TV or using other media, from computers to smart phones to tablets PCs, according to a new survey that found a child's use of media often reflects how much time parents spend in the similar way.

¨We generally found that media use is not a source of conflict in the home" for families with young children, Ellen Wartella, a researcher from Northwestem University, told USA Today. She led a survey of 2,326 parents who have children 8 and younger.It found that in 80 percent of families, children's media use was not a problem, with 55 percent “not too" or“ not at all"  concerned about it. It also showed parents have more positive than negative feelings about how media consumption affects a child's learning and the development of creativity.The exception is video games, which are viewed more negatively than TV, computers or mobile devices.“Parents rated video games as more likely to have a negative effect on children's school performance, attention time, creativity, social skills, behavior and sleep than any other medium," the researchers said in a news conference about the survey.

¨The findings exposes a generational shift (转移) in parental attitudes about technology's role in young children's lives," said Wartella.“Today's parents grew up with technology as a central pact of their lives, so they think about it differently than earlier generations of parents, instead of a battle with kids on one side and parents on the other, the use of media and technology has become a family affair. "

The researchers identified three media environments created by parents: media-centric (39 percent of families) , media-moderate (45%)and media-light (16%). Children  in media-centric families spend at least three hours more each day watching TV or using computers, video games and tablet PCs don't make parenting easier.And 88 percent of parents say they are most likely to turn to toys or activities to keep their children occupied.Slightly fewer turn to books (79%) and TV(78%).

The survey didn't look at how media affects children. That's a topic that the American Academy of Pediatrics has handled a number of times. The AAP says studies have found too much media use can lead to attention- problems, school difficulties, sleep and eating disorders and being fat. In addition, the Internet and cell phones can provide platforms for illegal and risky behaviors.¨By limiting screen time and offering educational media and non-electronic formats (格式)such as books, newspapers and board games, and watching television with their children, parents can help guide their children's media experience. Putting questionable content into context and teaching kids a700ut advertising contributes to their media literacy (素养) ," it says.

The pediatricians' group says parents should have “screen-free zones"  and TV should be turned off during dinner. At most, it recommends children and teens engage with entertainment media for no more than two hours a day and that should be high-quality content. It is important for kids to spend time on outdoor play, reading, hobbies  and  using their imaginations  in free  play.“ Kids  under 2 should not use television and other entertainment media because their brains are developing quickly and they learn best from direct human interaction," the group says.

An article on screen time by t.he Mayo Clinic also notes problems linked t.o over screen time, including  being  fat, irregular  sleep , behavioral  problems , weak  school  performance , violence  and  less time for active and creative play.

小题1:Parents have more negative than positive feelings about media consumption like    

A.computers

B.smart phones

C.video games

D.tablets PCs小题2:Most parents don't worry about kid's media use because        

A.they can limit the screen time

B.they want their children happy

C.they also grew up with technology

D.they can teach their children themselves小题3:From the data of the survey, we learn       

A.children in media-centric families are smarter than others

B.children in media-light families spend one hour watching TV

C.more than half of the parents think children's media use was a problem

D.media-centric children spend more than three hours each day on media use小题4:To make parenting easier, most parents probably        

A.try to persuade their children to read books

B.ask their children questions while watching TV

C.allow their children watching TV or using computers

D.turn to toys or activities to keep their children occupied小题5:Which of the following is a suggestion by the researchers?

A.Media use time for babies under 2 should be limited.

B.Entertainment media use should be high-quality content.

C.Schools should provide more time for active and creative play.

D.Home media use should provide platforms for illegal and risky behaviors.

题型:选择题

票据挂失止付的通知对象有()。

A、支票丧失,应由失票人通知出票人的开户银行办理挂失止付

B、银行承兑汇票挂失,应由失票人通知承兑银行办理挂失止付

C、商业承办兑汇票丧失,应由失票人通知承兑人办理挂失止付

D、现金银行汇票丧失,应由失票人通知汇票上记载的代理付款行办理挂失止付

E、现金银行本票丧失,应由失票人通知出票行办理挂失止付

题型:选择题

职业体育活动的主要承担机构是()。

A、健身俱乐部

B、半职业性体育俱乐部

C、职业体育俱乐部

D、球类俱乐部

题型:选择题

最新型接收机的NF值为()dB到()dB。

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