问题 选择题

当杠杆水平平衡时,L1>L2,若F1和F2的大小和方向都不变,将它们的作用点同时远离支点相同的距离,那么杠杆将(  )

A.F1那端下降

B.F2那端下降

C.仍然平衡

D.无法判断

答案

原来平衡时,F1L1=F2L2

因为L1>L2,所以F1<F2

设移动相同的距离x

则F1这一端:F1(L1+x)=F1L1+F1x

F2这一端,F2(L2+x)=F2L2+F2x

所以F1(L1+x)<F2(L2+x)

所以F2这一端下降.

故选B.

完形填空

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

Currently, there is a growing recognition that parental involvement is one key to student achievement.小题1:_____.However, while these may be important for developing a sense of community and parental ownership of the school and its issues, such activities do not translate directly to students achievement.

小题2:_____.Simply asking the question,” So, what did you do in school today?” can start a discussion between parent and child about topics studied in class.Even talks at home about less classroom-specific topics that interest the student are shown to be important to raising student achievement.小题3:____.Teachers can provide students with interesting ideas for starting school-related conversations at home.小题4:____.

The school’s focus should be on how to enable parents and their children to have such meaningful conversations about the topics and ideas flowing from the classroom.小题5:_____.

Finding ways to promote direct parent participation in their children’s lives-at school and at home will have a much greater impact.

A.Some parents expect too much of their children

B.Teenagers can have rich and interesting conversations if encouraged

C.Starting a parent council may not be a top priority

D.Many schools have attempted to find ways for parents to participate in school management by setting up parent councils for parents to volunteerE.Self-education plays an important role in children’s development

F.Another way for parents to be more active in their children’s education pays dividents

G.Telling children that school is valuable is a lot less effective than showing them it is by being involved in what they are doing there.

单项选择题