Some people have very good memories and can easily learn quite long poem（诗歌）by heart. Some people have1memories and can only2things that they have said again and again.
The3English writer Charles Dickens said that he could walk down 4 street in London and then tell you the name of every shop on5sides of the street. Great men in the world have wonderful memories.
A good memory is a great help in learning a language. Everybody learns 6language by remembering what he hears7he is a small child. Some children live with their parents in foreign countries and they seem8two languages as9as one. In school it is not so easy to learn foreign languages10students have little time11 it and they are busy with other subjects as well.
A man's mind is quite like a camera but it12photos of what we see and it can also take photos of what we feel, hear, smell and taste. When we take a real photo13a camera there is much work14before the photo is finished and ready to show to our friends.15 the same way there is much work to do before we can keep a picture forever in our mind.
，它在一定条件下可能发生的反应是