问题 单项选择题 A型题

青霉素G在碱性溶液中加热生成()

A.青霉素G钠

B.青霉二酸钠盐

C.生成6-氨基青霉素烷酸(6-APA.

D.β-内酰胺环水解开环

E.青霉醛和D-青霉胺

答案

参考答案:E

解析:青霉素在碱性条件或β-内酰胺酶作用下,β-内酰胺环裂环生成青霉酸,青霉酸在加热时失去二氧化碳,生成青霉噻唑酸,遇二氯化汞进一步分解生成青霉胺和青霉醛。青霉素在酸性条件下不稳定,分解反应比较复杂;在稀酸性溶液中(pH4.0)室温下,经分子内重排反应,生成青霉二酸,再进一步分解生成青霉醛和青霉胺。

阅读理解

阅读理解。

     Memory is the ability to keep track of things that have happened in the past. Memory really 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 how 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 a 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.

1. 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

2. The way to pick out the items on the first list from the second is known as ________ .        

A. recognition        

B. recall              

C. memorization      

D. relearning

3. What is considered as a measure of how much one has remembered?          

A. The length of the list.                      

B. The type of list items.

C. The time difference of relearning.            

D. The time difference of brain working.

4. A good way to train an animal to do something quickly is to ________.        

A. make the action easy                      

B. praise it in words

C. reward it with food                        

D. weaken its motivation

单项选择题