阅读理解
Fear and its companion pain are two of the most useful things that men and animals possess,if they
are properly used.If fire did not hurt when it burnt,children would play it until their hands were burnt
away.Similarly,if pain existed but fear did not,a child would burn itself again and again,because fear
would not warn the child to keep away from the fire that had burnt him or her before.A really fearless
soldier-and some do exist-is not a good soldier because he is soon killed; and a dead soldier is of no
use to his army.Fear and pain are therefore two guards without which men and animals might soon die
out.
In our first sentence we suggested that fear ought to be properly used.If,for example,you never go
out of your house because of the danger of being knocked down and killed in the street by a car,you
are letting fear rule you too much.Even in your house you are not absolutely safe:a plane may crash on
your house,or ants may eat away some of the wood in your roof,and they later may fall on you,or you
may get cancer!
The important thing is not to let fear rule you,but instead to use fear as your servant and guide.Fear
will warn you of dangers; then you have to decide what action to take.
In many cases,you can take quick and successful action to avoid the danger.For example,you see a
car coming straight towards you; fear warns you,you jump out of the way,and all is OK.
In some cases,however,you decide that there is nothing that you can do to avoid the danger.For
example,you cannot prevent a plane from crashing into your house,and you may not want to go and live
in a desert where there are no plants.In this case,fear has given you its warning; you have examined it
and decided on your course of action,so fear of this particular danger is no longer of any use to you,and
you have to try to overcome it.
1. Children would play with fire until their hands were burnt away if________.
A. they were given no warning beforehand
B. they didn't have any sense of pain at all
C. they had never burnt themselves
D. they felt afraid of the fire
2. A really fearless soldier________.
A. is of a little use to his army
B. is not afraid of battles at all
C. is nothing but a dead soldier
D. is easy to get killed in a battle
3. People sometimes succeed in timely avoiding dangers because________.
A. they are warned of the danger and take quick action
B. they are quick both in mind and in action
C. they are calm in face of danger
D. they have gained much experience
4. It is implied but not stated that________.
A. fear is always something helpful
B. too much fear is harmful
C. fear should be used as a servant and guide
D. fear is something strange and particular
，负 B.
，负 D.
＝|q|vB，由电流的微观表达式知：I＝|q|nSv＝|q|nabv，联立可得n＝
，故选C正确．