65A.option B.methodC.proposalD.data

The immune system is equal incomplexity to the combined intricacies of the brain and nervous system. Thesuccess of the immune system in defending the body relies on a dynamicregulatory com- munication network consisting of millions and millions ofcells. Organized into sets and subsets,these cells pass information back andforth like clouds of bees flying around a hive (蜂巢). The result is a sensitive system of checks andbalances that produces an immune response that is prompt, appropriateeffective, and self-limiting.

At the heart of the immunesystem is the ability to distinguish between self and nonself. When im- munedefenders encounter cells or organisms carrying foreign or nonselfmolecules,the immune troops move quickly to eliminate the intruders(入侵者). Virtually everybody cell carries distinctive molecules that identify it as self. The body's immunedefenses do not normally attack tissues that carry a self-marker. Rather,immune cells and other body cells coexist peaceably in s state known asself-toler- ance. When a normally functioning immune system attacks a nonselfmolecule, the system has the abil- ity to"remember" the specifics ofthe foreign body. Upon subsequent encounters with the same species ofmolecules, the immune system reacts accordingly. With the possible exception ofantibodies(抗体)

passed during lactation (哺乳期),this so called immune system memory is notinherited. Despite the occurrence of a virus in your family, your immune systemmust "learn" from experience with the many millions of distinctivenonself molecules in the sea of microbes(微生物)in which we live. Learning en- tails producing theappropriate molecules and cells to match up with and counteract each nonselfinvader.

Any substance capable oftriggering an immune response is called an antigen(抗原). Antigens are notto be confused with allergens (过敏原), which are most often harmless substances that provoke the immunesystem to set off the inappropriate and harmful response known as allergy. Anantigen can be a virus, a bacterium or even a portion or product of one ofthese organisms. Tissues or cells from another individual also act as antigens;because the immune system recognizes transplanted tissues as foreign, itrejects them. The body will even reject nourishing proteins unless they arefirst brokendown by the digestive system into their primary, nonantigenicbuilding blocks. An antigen announces its for- eignness by means of intricateand characteristic shapes called epitopes(抗原表位) , which protrude(突出) from its surface. Most antigens, even thesimplest microbes, carry several different kinds of epitopes on their surface;some may even carry several hundreds. Some epitopes will be more effective thanothers at stimulating an immune response. Only in abnormal situation does theimmune system wrongly identify self as nonself and execute a misdirected immuneattack.

What is used to describe the communication network consisting of cells in theimmune system？

A.The immune system's memory

B.Immune troops eliminating intruders

C.Bees flying around a hiv

D.A sea of microbes

A.Right

B.Wrong

C.Not mentioned

A.turning

B.jumping

C.shouting

D.shaking

A.great

B.strong

C.high

D.deep

Everyone can dream. Indeed,everyone does dream. Those who____ (51) that they never dream at all actuallydream_____ (52) as frequently as the rest of us,____ (53) they may not rememberanything about it. Even those of us who are perfectly ____ (54) of dreamingnight ____ (55) night very seldom remember those dreams in____ (56) detail butmerely retain an untidy mixture of seemingly unrelated impressions. Dreams arenot simply visual-we dream with all our ____ (57) , so that we appear toexperience sound, touch, smell, and taste.

One of the worjd's oldest____. (58) written documents is The 'Egyptian Book of Dreams. This volume isabout five thousand years old, so you can ____ (59) that dreams were believedto have a special significance even then. Many ancient civilizations believedthat you ____ (60) never wake a sleeping person as, during sleep, the soul hadleft the body and might not be able to return ____ (61) time if the sleeper were suddenly ____ (62).

Fromancient times to the present____ (63) , people have been ____ (64) attempts toin-terpret dreams and to explain their significance. There are man y booksavailable on the subject of dream interpretation, although unfortunately thereare almost as many meanings for a particular dream____ (65) there are books.

A. demand

B.promise

C.agree

D.claim

A.Other scientists are now searching for evidence to prove this

B. A Swiss writer named Erich Von Daniken wrote that the Nazca lines were designed as a landing place for UFOs

C.Scholars differ in interpreting the purpose of the designs.

D.The largest pictures may have been the sites for special ceremomes

E.Seen from the ground, it looks like lines scratched into the earth

F.He called Nazca "the largest astronomy book in the world"

DNA is the genetic material found within the cell nuclei of all livingthings. In mammals(哺乳动物)the strands of DNA are grouped into structures called chromosomes(染色体). With the exceptionof identical twins, the complete DNA of each individual is unique.

DNA fingerprinting is sometimes called DNAtyping. It is a method of identification that compares bits of DNA. A DNAfingerprint is constructed by first drawing out a DNA sample from body tissueor fluid such as hair, blood, or saliva(唾液). The sample is then segmented using enzymesc酶) , and the segmentsare arranged by size. The segments are marked with probes and exposed on X-rayfilm,where they form. a pattern of black bars-the DNA fingerprint. If the DNAfingerprints produced from two different samples match, the two samplesprobably came from the same person.

DNA fingerprinting was firstdeveloped as an identification technique in 1985. Originally used to detect thepresence of genetic diseases, it soon came to be used in criminalinvestigations and legal af-fairs. The first criminal conviction based on DNAevidence in theUnited Statesoccurred in 1988. In criminalinvestigations, DNA fingerprints derived from evidence collected at the crimescene are com-pared to the DNA fingerprints of suspects. Generally, courts haveaccepted the reliability of DNA tes-ting and admitted DNA test results intoevidence. However, DNA fingerprinting is controversial in a number of areas:the accuracy of the results, the cost of testing, and the possible misuse of thetech-nique.

The accuracy of DNAfingerprinting has been challenged for several reasons. First, because DNAsegments rather than complete DNA strands are "fingerprinted"; a DNAfingerprint may not be unique; large-scale research to confirm the uniquenessof DNA fingerprinting test results has not been conducted. In addition, DNAfingerprinting is often done in private Iaboratories that may not followuniform. testing standards and quality controls. Also, since human beings mustinterpret the test, human error could lead to false results.

DNA fingerprinting isexpensive. Suspects who are unable to provide their own DNA to experts may notbe able to successfully defend themselves against charges based on DNAevidence.

Widespread use of DNA testingfor identification purposes may lead to the establishment of a DNA fingerprintdatabase.

If two sisters are identical twins, their complete DNAs are

A.the same

B.unique

C.different

D.similar

A.untouched

B.certain

C.doubtful

D.silent

Influenza has been with us a long time. According to some Greek writers

(5l)medical history,the outbreak 0f 412 B. C. was of influenza. The same has been suggested of the sickness _(52)sweptthrough the Greek army attacking Syracuse in 395 B. C. Influenza is a disease that moves most quicklyamong people living in _ (53)conditions, hence,it is likely to attack armies. _(54)the nineteenth century there were five widespread outbreaks of influenza The last of thefive _(55)in 1889 and marked the beginning of the story of influenza in our time. _(56)therecent outbreak,it started in Asia.

For more than forty years before that outbreak,influenza had steadily . (57)and was be-lieved to be dying out. A new group of outbreaks was _(58)by the great outbreak of 1889-1890 and for the next quarter of a century influenza remained a constant threat.

In April 1918 influenza broke out among American troops stationed in France. It quickly spreadthrough all the _(59)but caused relatively few deaths. Four months later, however, a secondoutbreak started which _(60)to be a killer. It killed not only the old and already sick but alsohealthy young adults. It _(6l)through every country in the world,only a few distant islands inthe South Atlantic and the Pacific remaining _(62). It brought the life of whole countries tostop, food _(63)stopped and work loss was very great. Before the great outbreak ended,it hadkilled at (64)15 million people. Thereafter,there have been several great outbreaks throughout theworld. It is thus _ (65)that influenza is a terrible infection that we have to pay more attention to

51

A.on

B.by

C.to

D.with

A.advances in AIDS treatment are too slow

B.AIDS is their top concern.

C.the country spends too little on AIDS

D.AIDS deaths fell sharply