Supernovas in the Milky Way are the likeliest source for most of the cosmic rays reaching Earth. However, calculations show that supernovas cannot produce ultrahigh-energy cosmic rays (UHECRs), which have energies exceeding \(10^18\) electron volts. It would seem sensible to seek the source of these in the universe’s most conspicuous energy factories: quasars and gamma-ray bursts billions of light-years away from Earth. But UHECRs tend to collide with photons of the cosmic microwave background—pervasive radiation that is a relic of the early universe. The odds favor a collision every 20 million light-years, each collision costing 20 percent of the cosmic ray’s energy. Consequently, no cosmic ray traveling much beyond 100 million light-years can retain the energy observed in UHECRs.
Question 1
It can be inferred that the author of the passage would agree with which of the following about the origin of UHECRs that reach Earth?
A. The origin is something other than supernovas in the Milky Way.
B. The origin is most likely something other than very distant quasars or gamma-ray bursts.
C. The origin is most likely no more than a little over 100 million light-years away from Earth.
Question 2
In the context of the author's argument, the last sentence performs which of the following functions?
A. It explains a criterion that was employed earlier in the argument.
B. It shows that an apparently plausible position is actually self-contradictory.
C. It is a conclusion drawn in the course of refuting a potential explanation.
D. It overturns an assumption on which an opposing position depends.
E. It states the main conclusion that the author is seeking to establish.
The massive influx of women cyclists—making up at least a third of the total market— was perhaps the most striking and profound social consequence of the mid-1890s cycling boom. Although the new, improved bicycle had appealed immediately to a few privileged women, its impact would have been modest had it not attracted a greater cross section of the female population. It soon became apparent that many of these pioneer women bicyclists had not taken up the sport as an idle pastime. Rather, they saw cycling as a noble cause to be promoted among all women as a means to improve the general female condition. Not only would cycling encourage healthy outdoor exercise, they reasoned, it would also hasten long-overdue dress reform. To feminists, the bicycle affirmed nothing less than the dignity and equality of women.
Question 3
Which of the following statements about women cyclists is supported by the passage?
A. The newly improved bicycle of the mid-1890s appealed mostly to women in a privileged position.
B. The great majority of women in the mid-1890s considered cycling an idle pastime.
C. Women bicyclists promoted cycling as a healthy form of outdoor exercise.
Question 4
Which of the following does the passage suggest about pioneer women cyclists?
A. They saw cycling as a means to promote the advancement of women.
B. They argued that cycling would encourage women to get involved in a variety of noble causes.
C. They provided several reasons for a cross section of the female population to use the bicycle.
Question 5
Which of the following best describes the function of the second sentence (“Although . . . population”)?
A. It corrects a common misconception regarding the use of the bicycle in the mid-1890s.
B. It elaborates on a claim made in the previous sentence regarding a social consequence of the cycling boom.
C. It provides a context in which to understand the increased popularity of bicycle riding among privileged women.
D. It explains why cycling attracted such a significant cross section of women.
E. It describes the demographic characteristics of the consumer market for bicycles in the mid-1890s.
What causes a helix in nature to appear with either a dextral "right-handed," or clockwise twist or a sinistral "left-handed," or counterclockwise' twist is one of the most intriguing puzzles in the science of form. Most spiral-shaped snail species are predominantly dextral. But at one time, handedness (twist direction of the shell) was equally distributed within some snail species that have become predominantly dextral or, in a few species, predominantly sinistral. What mechanisms, control handedness and keep left-handedness rare?
It would seem unlikely that evolution should discriminate against sinistral snails if sinistral and dextral snails are exact mirror images, for any disadvantage that a sinistral twist in itself could confer on its possessor is almost inconceivable. But left- and right-handed snails are not actually true mirror images of one another. Their shapes are noticeably different. Sinistral rarity might, then, be a consequence of possible disadvantages conferred by these other concomitant structural features. In addition, perhaps left- and right-handed snails cannot mate with each other, having incompatible twist directions. Presumably an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thus keeping the rare form rare or creating geographically separated right- and left-handed populations.
But this evolutionary mechanism combining dissymmetry, anatomy, and chance does not provide an adequate explanation of why right-handedness should have become predominant. It does not explain, for example, why the infrequent unions between snails of opposing hands produce fewer offspring of the rarer than the commoner form in species where each parent contributes equally to handedness. Nor does it explain why, in a species where one parent determines handedness, a brood is not exclusively right- or left-handed when the offspring would have the same genetic predisposition. In the European pond snail Lymnaea peregra, a predominantly dextral species whose handedness is maternally determined, a brood might be expected to be exclusively right- or left-handed--and this often occurs. However, some broods possess a few snails of the opposing hand, and in predominantly sinistral broods, the incidence of dextrality is surprisingly high.
Here, the evolutionary theory must defer to a theory based on an explicit developmental mechanism that can favor either right- or left-handedness. In the case of Lymnaea peregra, studies indicate that a dextral gene is expressed during egg formation; i.e., before egg fertilization, the gene produces a protein, found in the cytoplasm of the egg, that controls the pattern of cell division and thus handedness. In experiments,an injection of cytoplasm from dextral eggs changes the pattern of sinistral eggs, but an injection from sinistral eggs does not influence dextral eggs. One explanation for the differing effects is that all Lymnaea peregra eggs begin left-handed but most switch to being right-handed. Thus, the path to a solution to the puzzle of handedness in all snails appears to be as twisted as the helix itself.
Question 6
Which of the following would serve as an example of “concomitant structural features” (line 19) that might disadvantage a snail of the rarer form?
A. A shell and body that are an exact mirror image of a snail of the commoner form
B. A smaller population of the snails of the rarer form
C. A chip or fracture in the shell caused by an object falling on it
D. A pattern on the shell that better camouflages it
E. A smaller shell opening that restricts mobility and ingestion relative to that of a snail of the commoner form
Question 7
It can be inferred from the passage that a predominantly sinistral snail species might stay predominantly sinistral for each of the following reasons EXCEPT for
A. a developmental mechanism that affects the cell-division pattern of snails
B. structural features that advantage dextral snails of the species
C. a relatively small number of snails of the same hand for dextral snails of the species to mate with
D. anatomical incompatibility that prevents mating between snails of opposing hands within the species
E. geographic separation of sinistral and dextral populations
Question 8
The second paragraph of the passage is primarily concerned with offering possible reasons why
A. it is unlikely that evolutionary mechanisms could discriminate against sinistral snails
B. sinistrality is relatively uncommon among snail species
C. dextral and sinistral populations of a snail species tend to intermingle
D. a theory based on a developmental mechanism inadequately accounts for the predominance of dextrality across snail species
E. dextral snails breed more readily than sinistral snails, even within predominantly sinistral populations
Question 9
Which of the following accurately describes the relationship between the evolutionary and developmental theories discussed in the passage?
A. Although the two theories reach the same conclusion, each is based on different assumptions.
B. They present contradictory explanations of the same phenomenon.
C. The second theory accounts for certain phenomena that the first cannot explain.
D. The second theory demonstrates why the first is valid only for very unusual, special cases.
E. They are identical and interchangeable in that the second theory merely restates the first in less technical terms.
X-ray examination of a recently discovered painting—judged by some authorities to be a self-portrait by Vincent van Gogh—revealed an underimage of a woman’s face. Either van Gogh or another painter covered the first painting with the portrait now seen on the surface of the canvas. Because the face of the woman in the underimage also appears on canvases van Gogh is known to have painted, the surface painting must be an authentic self-portrait by van Gogh.
Question 10
The conclusion above is properly drawn if which of the following is assumed?
A. If a canvas already bears a painted image produced by an artist, a second artist who uses the canvas to produce a new painting tends to be influenced by the style of the first artist.
B. Many painted canvases that can be reliably attributed to van Gogh contain underimages of subjects that appear on at least one other canvas that van Gogh is known to have painted.
C. Any painted canvas incorrectly attributed to van Gogh would not contain an underimage of a subject that appears in authentic paintings by that artist.
D. A painted canvas cannot be reliably attributed to an artist unless the authenticity of any underimage that painting might contain can be reliably attributed to the artist.
E. A painted canvas cannot be reliably attributed to a particular artist unless a reliable x-ray examination of the painting is performed.
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