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We sometimes think humans are uniquely vulnerable to anxiety, but stress seems to affect the immune defenses of lower animals too. In one experiment, for example, behavioral immunologist (免疫学家）Mark Laudenslager, at the University of Denver, gave mild electric shocks to 24 rats. Half the animals could switch off the current by turning a wheel in their enclosure, while the other half could not. The rats in the two groups were paired so that each time one rat turned the wheel it protected both itself and its helpless partner from the shock. Laudenslager found that the immune response was depressed below normal in the helpless rats but not in those that could turn off the electricity. What he has demonstrated, he believes, is that lack of control over an event, not the experience itself, is what weakens the immune system.
Other researchers agree. Jay Weiss, a psychologist at Duke University School of Medicine, has shown that animals who are allowed to control unpleasant stimuli don't develop sleep disturbances or changes in brain chemistry typical of stressed rats. But if the animals are confronted with situations they have no control over, they later behave passively when faced with experiences they can control Such findings reinforce psychologists' suspicions that the experience or perception of helplessness is one of the most harmful factors in depression.
One of the most startling examples of how the mind can alter the immune response was discovered by chance. In 1975 psychologist Robert Ader at the University of Rochester School of Medicine conditioned (使形成条件反射）mice to avoid saccharin (糖精）by simultaneously feeding them the sweetener and injecting them with a drug that while suppressing their immune systems caused stomach upsets. Associating the saccharin with the stomach pains, the mice quickly learned to avoid the sweetener. In order to extinguish this dislike for the sweetener, Ader reexposed the animals to saccharin, this time without the drug, and was astonished to find that those mice that had received the highest amounts of sweetener during their earlier conditioning died. He could only speculate that he had so successfully conditioned the rats that saccharin alone now served to weaken their immune systems enough to kill them.
1
Laudenslager's experiment showed that the immune system of those rats who could turn off the electricity ____.
A.
was strengthened
B.
was not affected
C.
was altered
D.
was weakened
本题答案：
A
B
C
D
参考答案：
B
系统解析：
第1段第5句提到：Laudenslager发现那些无助的老鼠的免疫反应被削弱了，低于正常水平，而那些能切断电源的老鼠却没有。因此,B正确。
2
According to the passage, the experience of helplessness causes rats to ____.
A.
try to control unpleasant stimuli
B.
turn off the electricity
C.
behave passively in controllable situations
D.
become abnormally suspicious
本题答案：
A
B
C
D
参考答案：
C
系统解析：
根据文章第2段第3句:Jay Weiss的实验表明一旦动物遇到过它们控制不了的事情和局面，以后即使是面临它们能够控制的事情，它们的表现还是会很被动，C正确。A和B与文章所表达的意思不符；D在文 中并没有提及。
3
The reason why the mice in Ader's experiment avoided saccharin was that ____.
A.
they disliked its taste
B.
it affected their immune systems
C.
it led to stomach pains
D.
they associated it with stomachaches
本题答案：
A
B
C
D
参考答案：
D
系统解析：
根据文章末段：在实验中，老鼠被喂食了大量糖精，并注射能抑制其免疫系统功能的药物而造成胃疼。因此老鼠将糖精与胃疼联系起来，并迅速学会了不吃糖精，D与文中所表达的意思一致。A、B在文中并没有提及；文中提到是药物导致胃疼，而并非糖精，故C错。
4
The passage tells us that the most probable reason for the death of the mice in Ader's experiment was that ______.
A.
they had been weakened psychologically by the saccharin
B.
the sweetener was poisonous to them
C.
their immune systems had been altered by the mind
D.
they had taken too much sweetener during earlier conditioning
本题答案：
A
B
C
D
参考答案：
C
系统解析：
根据文章末段：心理能够改变免疫功能的最令人吃惊的例子就是Ader的实验。通过实验，Ader认为他已成功地使老鼠形成了一种条件反射，只要用糖精就能削弱老鼠的免疫功能，并足以杀死它们。因为在实验中， 老鼠将胃疼与糖精联系起来，再次看到糖精时，老鼠的心理变化破坏了它们的免疫系统，并导致了它们“ 死亡，因此C正确。糖精确实影响了它们的心理因素，但这并不是导致死亡的主要原因，A错。
5
It can be concluded from the passage that the immune system of animals _____.
A.
can be weakened by conditioning
B.
can be suppressed by drug injections
C.
can be affected by frequent doses of saccharin
D.
can be altered by electric shocks
本题答案：
A
B
C
D
参考答案：
A
系统解析：
Ader采用一定的方法使老鼠形成条件反射，这种反射削弱了老鼠的免疫功能。根据以上分析，A与文中所表达的意思一致;B与原文意思相悖；服用糖精影响免疫系统，是针对Ader实验中的老鼠而言，并不是针对所有动物,C错;D与文中内容不符。
If you go down to the woods today, you may meet high-tech trees—genetically modified to speed their growth or improve the quality of their wood. Genetically-engineered food craps have become increasingly common, albeit controversial, over the past ten years. But genetic engineering of trees has Iagged behind.
Part of the reason is technical. Understanding, and then altering, the genes of a big pine tree are more complex than creating a better tomato. While tomatoes sprout happily, and rapidly, in the laboratory, growing a whole tree from a single, genetically altered cell in a test tube is a tricky process that takes years, not months. Moreover, little is known about tree genes. Some trees, such as pine trees, have a lot of DNA—roughly ten times as much as human. And, whereas the Human Genome Project is more than half-way through its task of isolating and sequencing the estimated 100, 000 genes in human cells, similar efforts to analyze tree genes are still just saplings (幼苗).
Given the large number of tree genes and the little that is known about them, tree engineers are starting with a search for genetic “markers”. The first step is to isolate DNA from trees with desirable properties such as insect resistance. The next step is to find stretches of DNA that show the presence of a particular gene. Then, when you mate two trees with different desirable properties, it is simple to check which offspring contain them all by looking for the genetic markers. Henry Amerson, at North Carolina State University, is using genetic markers to breed fungal resistance into southern pines. Billions of these are grown across America for pulp and paper, and outbreaks of disease are expensive. But not all individual trees are susceptible. Dr. Amerson's group has found markers that distinguish fungus-resistant stock from disease-prone trees. Using traditional breeding techniques, they are introducing the resistance genes into pines on test sites in America.
Using genetic markers speeds up old-fashioned breeding methods because you no longer have to wait for the tree to grow up to see if it has the desired traits. But it is more a sophisticated form of selective breeding. Now, however, interest in genetic tinkering (基因修补）is also gaining ground. To this end, Dr. Amerson and his colleagues are taking part in the Pine Gene Discovery Project, an initiative to identify and sequence the 50,000-odd genes in the pine tree's genome. Knowing which gene does what should make it easier to know what to alter.
6
Compared with genetic engineering of food crops, genetic engineering of trees _____.
A.
began much later
B.
has developed more slowly
C.
is less useful
D.
was less controversial
本题答案：
A
B
C
D
参考答案：
B
系统解析：
本文并没有提到树木基因改良技术从什么时候开始，所以有可能树木的基因改良技术和别的基因改良技术在开始的时间上相差不大，但在所取得的成果方面却有很大的差别，因此，本题关键在于理解首段末句中的lag behind指的是程度上的落后，而非时间上的落后，故B正确。
7
What does the author think about the genetic engineering of pine trees?
A.
Time-consuming.
B.
Worthwhile.
C.
Significant.
D.
Technically impossible.
本题答案：
A
B
C
D
参考答案：
A
系统解析：
第2段第3句中的that takes years表明研究树木的基因改造技术将花费很长时间，因此选项A为本题答案。原文没有就选项B和C两方面做出讨论，因此不能推断出这两个选项；虽然第2段首句提到technical—词，但文章表明树木基因改造技术是可行的，只是会花费较多的时间，因此选项D也不正确。
8
What can we learn about the research on tree genes?
A.
The research methods are the same as the analysis of human genes.
B.
The findings are expected to be as fruitful as the analysis of human genes.
C.
It will take as much time and effort as the analysis of human genes.
D.
The research has been mainly concentrated on the genes of young trees.
本题答案：
A
B
C
D
参考答案：
A
系统解析：
第2段末句中的similar efforts指的就是task of isolating and sequencing,即分析基因的常用方法，该句表明人类基因和树种基因的分析方法相同，但进展有差别，因此选项A为正确的推断。
9
It is discovered by Henry Amerson's team that ____.
A.
southern pines cannot resist fungus
B.
all southern pines are not susceptible
C.
the genetic marker in southern pines was the easiest to identify
D.
fungus-resistant genes came originally from outside the U.S.A.
本题答案：
A
B
C
D
参考答案：
B
系统解析：
选项B是一个半否定的句式，因此本题关键在于理解选项B的All…are not… 结构在意义上等同于第3段例数第3句的not all... are...。第3段倒数第2句中的fungus-resistant, stock指的是南方松树中能抗真菌的树种，并非别的与南方松树毫不相关的树种，因此A的说法不正确。
10
What is the primary objective of carrying out the Pine Gene Discovery Project?
A.
To speed up old-fashioned breeding methods.
B.
To identify all the genes in the pine tree's genome.
C.
To find out what desired traits the pine trees have.
D.
To make it easier to know which gene needs altering.
本题答案：
A
B
C
D
参考答案：
B
系统解析：
末段倒数第2句中的an initiative是the Pine Gene Discovery Project的同位语，表明开展该计划的目的， 因此选项B为本题答案。其他选项都是在完成该计划后能够达成的工作，它们都要以松树基因的排列组合为基础，因此，这些选项都不是primary objective, 而是在实现primary objecive之后继续进行的工作。
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