Memory is the ability to keep track of things that have happened in the past. Memory reall

y is learning. One needs memory to ride a bicycle. A dog needs to remember if it is to come when called.

Memory is said to be stored in the brain as a "memory trace (记忆痕) ". What makes up this trace is not known. Some scientists believe that certain chemical substances may carry certain memories. For example, one substance, when given to rats, causes them to fear the dark.

Other research into memory has to do with how the brain works. Psychologists use three means to find out bow a person remembers. For example, give a person a grocery list. Let the person memorize the list, then put it away. The most natural way to find out how much a person remembers of the grocery list is to ask what he or she remembers. This is called the method of recall. Another method is called recognition. Give the person another grocery list. Ask him or her to choose items on the first list from the items that are on only the second list. Often a person will be able to recognize things that he or she cannot recall. A third method of finding how much a person remembers is called relearning. Here the person is asked to read over the first list. The person will probably learn the list the second time faster than he did the first time. The difference in the time it takes to relearn the list is thought of as measure of how much a person has remembered.

One way of remembering something is to repeat it many times. Interest is very important. Boring lists of facts are much more difficult to remember than something that we understand and are interested in. Motivation, or wanting to do something, is also important. Motivation is linked with reward. For example, a hungry animal quickly learns how to do something if that action gets the animal food. In humans, wanting to learn is often motivation. The praise of a teacher or the knowledge that an answer is correct is rewarding.

We can learn from the 2nd paragraph that ______.

A．bad memories may cause rats to fear the dark

B．it is hard to tell what a memory trace consists of

C．chemical substances carry certain memories

D．memory is stored in the brain as a substance