Sales of telephones have increased dramatically over the last year. In order to take advan

ief that

A．the space between the galaxies is devoid of matter.

B．the space between galaxies is occupied by stars that cannot be detected by optical photographs.

C．galaxies have decreased in mass by half since their formation.

D．galaxies contain stars, each the size of Jupiter, which form. clusters.

E．galaxies are being penetrated by gas forced out of other galaxies by supernova explosions.

the British colonists

A．collected tribute from the native population.

B．kept records from a very early date.

C．drove Native Americans off the land.

D．were unable to provide medical care against epidemic disease.

E．enslaved the native populations in America.

iversity of Virginia lectures in 1954?

A．Southern racial segregation was continuous and uniform.

B．Black people made considerable progress only after Reconstruction.

C．Jim Crow legislation was conventional in nature.

D．Jim Crow laws did not go as far in codifying traditional practice as they might have.

E．Jim Crow laws did much more than merely reinforce a tradition of segregation.

e a potential source of aid to a patient who was not adequately producing and releasing serotonin?

A．Meals consisting almost exclusively of protein.

B．Meals consisting almost exclusively of carbohydrates.

C．Meals that would elicit insulin secretion.

D．Meals that had very low concentrations of tyrosine.

E．Meals that had very low concentrations of leucine.

here in the body. In recent studies, however, we have discov- ered that the production and release in brain neurons of the neurotransmitter serotonin(neurotransmitters are compounds that neurons use to transmit signals to other cells)depend directly on the food that the body processes. Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryp-tophan increases. In later studies we found that injecting insulin into a rats bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animals own insulin similarly affected serotonin production. We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood trypto- phan level and the concentrations of tryptophan serotonin in the brain increased after the meal. Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell. Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryp- tophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood con- centration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein in the meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and re- leased.

Which of the following titles best summarizes the contents of the passage?

A．Neurotransmitters: Their Crucial Function in Cellular Communication

B．Diet and Survival: An Old Relationship Reexamined

C．The Blood Supply and the Brain: A Reciprocal Dependence

D．Amino Acids and Neurotransmitters: The Connection Between Serotonin Levels and Tyrosine

E．The Effects of Food Intake on the Production and Release of Serotonin: Some Recent Findings

cells are injured?

A．The flow of electrical impulses through nerve cells at the site of the injury is broken.

B．The production of substance P traveling through nerve cells to the brain increases.

C．Endorphins begin to speed up the response of nerve cells at the site of the injury.

D．A flood of prostaglandins sensitizes nerve endings at the site of the injury.

E．Nerve cells connected to the spinal cord become electrically quiescent.

According to information in the passage, the term "de-skilling" refers to the

A．loss of skills to industry when skilled workers are replaced by unskilled laborers.

B．substitution of mechanized processes for labor formerly performed by skilled workers.

C．labor theory that automation is technologically comparable to skilled labor.

D．process by which skilled machinists "teach" machines to perform. certain tasks.

E．exclusion of skilled workers from participation in the development of automated technology.

Which of the following best expresses the authors main point?

A．Americans" pride in their jobs continues to give them stamina today.

B．The absence of a status quo ante has undermined United States economic structure.

C．The free enterprise system has been only a useless concept in the United States.

D．The myth of the American free enterprise system is seriously flawed.

E．Fascination with the ideal of "openness" has made Americans a progressive people.

an illusion of protection. Quantities of such chemicals, already produced, exist as coolants in millions of refrigerators. When they reach the o-zone layer in the atmosphere, their action cannot be halted. So there is no way to prevent these chemicals from damaging the ozone layer further. Which of the following, if true, most seriously weakens the argument above?

A．It is impossible to measure with accuracy the quantity of ozone-destroying chemicals that exist as coolants in refrigerators.

B．In modern societies, refrigeration of food is necessary to prevent unhealthy and potentially life-threatening conditions.

C．Replacement chemicals that will not destroy ozone have not yet been developed and would be more expensive than the chemicals now used as coolants in refrigerators.

D．Even if people should give up the use of refrigeration, the coolants already in existing refrigerators are a threat to atmospheric ozone.

E．The coolants in refrigerators can be fully recovered at the end of the useful life of the refrigerators and reused.

they are to his mental and spiritual health. After all, he said, there must be something sound to any human practice that endures more than three thousand years of history. Which of the following, if true, is the strongest relevant objection to the argument the teacher makes on the basis of the time yoga has endured?

A．The teacher benefits by the teaching of yoga and so, as a beneficiary, is not a disinterested witness.

B．The practice of yoga has changed somewhat over three thousand years.

C．The teacher cites the experience of only one person, whose well-being might be due to other causes.

D．War, which cannot on balance be called sound, has lasted the length of human history.

E．Three thousand years is an underestimate of the time period.