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发表于 2012-2-29 22:20:19
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Questions 70-75 refer to the passage on page 386.
70. In the passage, the author is primarily interested in
(A) suggesting an alternative to an outdated
research method
(B) introducing a new research method that calls an
accepted theory into question
(C) emphasizing the instability of data gathered
from the application of a new scientific method
(D) presenting a theory and describing a new
method to test that theory
(E) initiating a debate about a widely accepted
theory
Main idea
This question concerns the main point of the
passage. A careful examination of the overall
structure of the passage will reveal the main
point. In the first paragraph, the author briefly
presents Milankovitch's theory and explains why
it could not be tested early on. In the second and
third paragraphs, the author describes how a new
method allows testing of the theory and shows
how evidence from the testing supports the
theory. While the final paragraph acknowledges
that other factors should be considered, the
author's primary interest in this passage is in
presenting Milankovitch's theory and the recently
discovered method for testing it.
A A new research method is described, but no
previous method is discussed.
B As described in the passage, the new
method tests and confirms the theory; there
is no mention that the theory is accepted or
that the method casts doubt on it.
C Nothing in the passage suggests that
"instability of data" is an issue.
D Correct. The author presents Milankovitch's
theory and describes the oxygen isotope
method of testing it.
E The theory is nowhere said to be "widely
accepted" and the author does not debate
the theory.
The correct answer is D.
71. The author of the passage would be most likely to
agree with which of the following statements about the
Milankovitch theory?
(A) It is the only possible explanation for the ice
ages.
(B) It is too limited to provide a plausible explanation
for the ice ages, despite recent research
findings.
(C) It cannot be tested and confirmed until further
research on volcanic activity is done.
(D) It is one plausible explanation, though not the
only one, for the ice ages.
(E) It is not a plausible explanation for the ice ages,
although it has opened up promising possibilities
for future research.
Application
The author's reaction to the statements about the
Milankovitch theory must be based on how the
author treats the theory in the passage. The first,
second, and third paragraphs describe the theory
and the use of a new research method to test the
theory. The passage states that data from these
tests have established a strong connection between
variations in the Earth's orbit and the periodicity of
the ice ages, suggesting that the author of the
passage believes the theory is plausible. In the
final paragraph, the author points to other factors
that might be involved, suggesting that the theory
might not provide a complete explanation.
A In the last paragraph, the author suggests
that because there are still other untested
factors that may have effects on climate,
other explanations are possible.
B Though in the last paragraph the author
points to other factors that may be involved,
these are not presented by the author as
indicating limitations that diminish the
plausibility of the theory—they are
acknowledged merely as possibilities that are
not now understood—and nothing else in
the passage suggests that the theory is "too
limited."
C The author shows how the theory has been
tested; volcanic activity is not part of this
theory.
D Correct. The author's presentation of the
theory and the tests of the theory show that
the author finds the theory plausible; the
mention of other factors shows the author
does not think that all other explanations
have been ruled out, even if they are as yet
untested.
E The theory was a plausible explanation from
its beginning, but it was not testable until
recently; scientists would be unlikely to try
to devise means to test a theory that did not
strike them as antecedently plausible.
The correct answer is D.
72. It can be inferred from the passage that the isotope
record taken from ocean sediments would be less
useful to researchers if which of the following were true?
(A) It indicated that lighter isotopes of oxygen
predominated at certain times.
(B) It had far more gaps in its sequence than the
record taken from rocks on land.
(C) It indicated that climate shifts did not occur
every 100,000 years.
(D) It indicated that the ratios of oxygen 16 and
oxygen 18 in ocean water were not consistent
with those found in fresh water.
(E) It stretched back for only a million years.
Inference
To make an inference about the isotope record
from ocean sediments, examine what the passage
says about that record. The third paragraph
discusses that record and lists its two advantages.
First, it is a global record with remarkably little
variation in samples from varied locations.
Second, it is more continuous than the record from
rocks. If either of these advantages were not true,
then it is logical to infer that the record would be
less useful.
A According to lines 14-16, the lighter isotope
does predominate; this is part of the record
and does not affect its usefulness.
B Correct. In lines 37-42, the author states
that an advantage of the ocean record is that
it is a more continuous record than that taken
from rocks on land. If this were not true, the
ocean record would be less useful.
C If the record were to show that the shifts did
not occur every 100,000 years,
Milankovitch's theory would be weakened.
This impact on the theory does not make
the isotope record less useful to researchers.
The record is useful precisely because it can
offer evidence to confirm or refute such
theories.
D This inconsistency would not affect the
usefulness of the ocean-water record.
Researchers would simply need to
accommodate the fresh-water inconsistency.
E The record would still be useful. Lines
42-46 attest to the establishment of a
pattern based on data from the past several
hundred thousand years.
The correct answer is B.
73. According to the passage, which of the following is
true of the ratios of oxygen isotopes in ocean
sediments?
(A) They indicate that sediments found during an ice
age contain more calcium carbonate than
sediments formed at other times.
(B) They are less reliable than the evidence from
rocks on land in determining the volume of
land ice.
(0 They can be used to deduce the relative volume
of land ice that was present when the sediment
was laid down.
(D) They are more unpredictable during an ice age
than in other climatic conditions.
(E) They can be used to determine atmospheric
conditions at various times in the past.
Supporting ideas
The phrase according to the passage suggests that
the answer to the question is most likely stated in
the passage. Lines 12-14 state that the relative
volume of land ice can be deduced from the ratio
of oxygen 18 to oxygen 16 in ocean sediments.
A There is no evidence in the passage about
this point.
B The ocean record is described in lines 38-39
as more continuous, so it is unlikely to be less
reliable. In any case, reliability is not
discussed.
C Correct. Lines 12-14 explain that the land-
ice volume for a given period can be deduced
from the ratio of two oxygen isotopes.
D There is no evidence in the passage to
support this statement.
E The passage does not discuss the use of this
record in determining past atmospheric
conditions.
The correct answer is C.
74. It can be inferred from the passage that precipitation
formed from evaporated ocean water has
(A) the same isotopic ratio as ocean water
(B) less oxygen 18 than does ocean water
(0 less oxygen 18 than has the ice contained in
continental ice sheets
(D) a different isotopic composition than has
precipitation formed from water on land
(E) more oxygen 16 than has precipitation formed
from fresh water
Inference
Any inference about precipitation from
evaporated ocean water needs to be based on what
the passage says. Lines 20-22 show that heavier
isotopes tend to be left behind when water evaporates
from the ocean surfaces. Therefore, the evaporated
water would contain less oxygen 18 and the
remaining ocean water would contain more. It is
logical to infer that precipitation formed from this
evaporated water would also contain less oxygen
18.
A Lines 20-24 explain that the water
remaining in the ocean after evaporation has
more oxygen 18.
B Correct. Since the heavier isotopes tend to be
left behind, there will be less oxygen 18 in
the evaporated water and in the precipitation
that forms from it.
C The passage suggests that the ocean water
evaporates and through subsequent
precipitation helps form the ice sheets, so
the amount of oxygen 18 in the ice sheets
should be similar to the amount in the
precipitation formed from the evaporated
water.
D The passage does not discuss precipitation
formed from water on land.
E The passage does not discuss precipitation
formed from fresh water.
The correct answer is B.
75. It can be inferred from the passage that calcium
carbonate shells
(A) are not as susceptible to deterioration as rocks
(B) are less common in sediments formed during an
ice age
(0 are found only in areas that were once covered
by land ice
(D) contain radioactive material that can be used to
determine a sediment's isotopic composition
(E) reflect the isotopic composition of the water at
the time the shells were formed
Inference
Any inference about calcium carbonate shells
needs to be based on what the passage says about
these shells. Lines 24-32 explain the role of these
shells in forming sediments and establishing a
chronology for ice ages. The shells were constructed
with oxygen atoms drawn from the surrounding
ocean. Lines 29-32 make it clear that if the
sediments reveal a higher ratio of oxygen 18, it is
because more oxygen 18 had been left behind
when the ocean water evaporated and contributed
to the growth of continental ice sheets. It can thus
be inferred that the shells that make up those
sediments must reflect the proportion of oxygen
18 found in the ocean water at the time they were
formed.
A The only mention of rocks in the passage is a
comparison of "gappiness" of the rock and
sedimentary specimen records in lines
38—39; this information does not allow any
firm inference to be made with respect to
relative susceptibility to deterioration,
though a more continuous record might be
the result of less susceptibility to
deterioration.
B The passage does not make any reference to
the relative abundance of these shells during
ice ages; no such inference can be drawn.
C The only information in the passage that
might support this statement is found in
lines 29-32, but that information, about the
correlation between oxygen ratios in
sediment specimens and land ice, describes a
relation that implies nothing about
distributions of such specimens.
D Though the passage does indirectly indicate
that the shells contained radioactive
material, nothing in the passage suggests
that radioactive material is used to
determine isotopic composition.
E Correct. The passage explains that oxygen
atoms in the surrounding water are one of
the building blocks of calcium carbonate
shells. The isotopic composition of the
surrounding water changes during the ice
age cycles, so it is logical that the isotopic
composition of the shells will change
depending on when they were formed. |
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发表于 2012-2-29 22:19:40
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