问题 选择题
电气化铁路的输电线常用图所示的方式悬挂在钢缆上.钢缆的A端固定在电杆上,B端连接在滑轮组上.滑轮组由a、b、c三个滑轮构成,配重P由多个混凝土圆盘悬挂在一起组成,配重的总重为G,若不计摩擦和滑轮的重量,则以下说法中正确的是(  )

A.a为动滑轮,B端钢缆受到滑轮组的拉力大小约为3G

B.a为动滑轮,B端钢缆受到滑轮组的拉力大小约为G

C.a、c为动滑轮,B端钢缆受到滑轮组的拉力大小约为3G

D.a、c为动滑轮,B端钢缆受到滑轮组的拉力大小约为G

答案

答案:A

阅读理解

Habits,whether good or bad,are gradually formed when a person does a certain thing again.He is driven by some unseen force to do the same thing repeatedly, and then a habit is formed.Once a habit is formed,it is difficult,and sometimes impossible,to get rid of.It is therefore very important that we should pay great attention to the formation of habits.Children often form bad habits, some of which remain with them as long as they live older. Persons also form bad habits lasting as long as they live,and sometimes become ruined by them

There are other habits which,when formed in early life,are of great help.Many successful men say that much of their success has something to do with certain habits in early life,such as early rising,honesty and so on.

Among the habits which children should not form are laziness,lying,stealing and so on.These habits are all easily formed.Unfortunately older persons often form habits which could have been avoided.

We should keep away from all these bad habits,and try to form such habits as will be good for ourselves and others.

小题1:      are formed little by little.

A.Good habits

B.Bad habits

C.Both good habits and bad habits

D.Neither good habits nor bad habits小题2:The underlined word“them”in the first paragraph refers to_______.

A.bad habits

B.good habits

C.children

D.other persons小题3:Generally speaking, it’s difficult for one______ and easy for them______ which should be avoided.   

A.to form bad habits;to form good habits

B.to form good habits;to form bad habits

C.to form such habits as wilI be good;to get rid of bad habits

D.to get rid of bad habits;to form good habits

单项选择题