Of all the areas of learning the most important is the development of attitudes. Emotional reactions as well as logical thought processes affect the behavior of most people.
"The burnt child fears the fire" is one instance; another is the rise of despots like Hitler. Both examples also point up the fact that attitudes stem from experience. In one case the experience was direct and impressive; in the other it was indirect and cumulative. The Nazis were indoctrinated largely by the speeches they heard and the books they read.
The classroom teacher in the elementary school is in a strategic position to influence attitudes. This is true partly because children acquire attitudes from those adults whose word they respect.
Another reason it is true is that pupils often delve somewhat deeply into a subject in school that has only been touched upon at home or has possibly never occurred to them before. To a child who had previously acquired little knowledge of Mexico, his teacher’s method of handling such a unit would greatly affect his attitude toward Mexicans.
The media through which the teacher can develop wholesome attitudes are innumerable. Social studies (with special reference to races, creeds and nationalities), science matters of health and safety, the very atmosphere of the classroom... these are a few of the fertile fields for the inculcation of proper emotional reactions.
However, when children come to school with undesirable attitudes, it is unwise for the teacher to attempt to change their feelings by cajoling or scolding them. She can achieve the proper effect by helping them obtain constructive experiences.
To illustrate, first grade pupils afraid of policemen will probably alter their attitudes after a classroom chat with the neighborhood officer in which he explains how he protects them. In the same way, a class of older children can develop attitudes through discussion, research, outside reading and all-day trips.
Finally, a teacher must constantly evaluate her own attitudes, because her influence can be deleterious if she has personal prejudices. This is especially true in respect to controversial issues and questions on which children should be encouraged to reach their own decisions as a result of objective analysis of all the facts.

The central idea of the above passage is that ______.

A．attitudes affect our actions

B．teachers are important in developing or changing pupils’ attitudes

C．attitudes can be changed by some classroom experiences

D．by their attitudes, teachers inadvertently affect pupils’ attitudes

在弹性形变范围内，弹簧的伸长跟加在它上面的拉力成正比，利用这一原理可制作弹簧测力计。

（1）现给你提供：一根带有指针和挂钩的弹簧、一块上方钉有一个小钉子并且表面贴有白纸的长方形小木板、已知重量为G的钩码若干个和笔。请你利用上述提供的器材，自制一个弹簧测力计，根据你的制作过程，请回答：弹簧测力计的刻度是怎样标出来的。

（2）若此弹簧测力计的量程为5N，现要利用它测量形状不规则、密度约为2×10³kg/m³、重约为15N物体的实际重量，可利用的器材有：一根硬棒（自身重力不计）、能承受较大拉力的细线、海棉、一长方体木块、刻度尺、烧杯、水。请选出你所需要的器材，用此弹簧测力计测量此物体的实际重量（可画出必要的示意图），请写出：

① 选用的器材：

② 主要的实验步骤：

③ 物体重量的数学表达式：