GMAT综合阅读精解之十六!GMAT阅读作为GMAT考试的重要组成部分,其对GMAT分数有着较大的影响。考生要想提高GMAT总分,对GMAT阅读部分不容忽视,接下来小编将为大家分享GMAT综合阅读精解的第十六部分,一起来看一下。

  Milankovitch proposed in the early twentieth century

  that the ice ages were caused by variations in the Earth’s

  orbit around the Sun. For sometime this theory was

  considered untestable, largely because there was no suffi-

  (5) ciently precise chronology of the ice ages with which

  the orbital variations could be matched.

  To establish such a chronology it is necessary to

  determine the relative amounts of land ice that existed

  at various times in the Earth’s past. A recent discovery

  (10) makes such a determination possible: relative land-ice

  volume for a given period can be deduced from the ratio

  of two oxygen isotopes, 16 and 18, found in ocean sedi-

  ments. Almost all the oxygen in water is oxygen 16, but

  a few molecules out of every thousand incorporate the

  (15) heavier isotope 18. When an ice age begins, the conti-

  nental ice sheets grow, steadily reducing the amount of

  water evaporated from the ocean that will eventually

  return to it. Because heavier isotopes tend to be left

  behid when water evaporates from the ocean surfaces,

  (20) the remaining ocean water becomes progressively

  enriched in oxygen 18. The degree of enrichment can

  be determined by analyzing ocean sediments of the

  period, because these sediments are composed of calcium

  carbonate shells of marine organisms, shells that were

  (25) constructed with oxygen atoms drawn from the sur-

  rounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice

  there was when the sediment was laid down.

  As an indicator of shifts in the Earth’s climate, the

  (30) isotope record has two advantages. First, it is a global

  record: there is remarkably little variation in isotope

  ratios in sedimentary specimens taken from different

  continental locations. Second, it is a more continuous

  record than that taken from rocks on land. Because of

  (35) these advantages, sedimentary evidence can be dated

  with sufficient accuracy by radiometric methods to

  establish a precise chronology of the ice ages. The dated

  isotope record shows that the fluctuations in global ice volume over the past several hundred thousand years

  (40) have a pattern: an ice age occurs roughly once every

  100,000 years. These data have established a strong

  connection between variations in the Earth’s orbit and

  the periodicity of the ice ages.

  However, it is important to note that other factors,

  (45) such as volcanic particulates or variations in the amount

  of sunlight received by the Earth, could potentially have

  affected the climate. The advantage of the Milankovitch

  theory is that it is testable: changes in the Earth’s orbit

  can be calculated and dated by applying Newton’s laws

  (50) of gravity to progressively earlier configurations of the

  bodies in the solar system. Yet the lack of information

  about other possible factors affecting global climate does

  not make them unimportant.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  (C) 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.

  5. 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

  (C) 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

  6. According to the passage, which of the following is (are)

  true of the ice ages?

  Ⅰ. The last ice age occurred about 25,000 years ago.

  Ⅱ. Ice ages have lasted about 10,000 years for at least

  the last several hundred thousand years.

  Ⅲ. Ice ages have occurred about every 100,000 years

  for at least the last several hundred thousand years.

  (A) Ⅰ only

  (B) Ⅱ only

  (C) Ⅲ only

  (D) Ⅰand only

  (E) Ⅰ,Ⅱ and Ⅲ

  7. 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

  (C) 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

  8. The purpose of the last paragraph of the passage is to

  (A) offer a note of caution

  (B) introduce new evidence

  (C) present two recent discoveries

  (D) summarize material in the preceding paragraphs

  (E) offer two explanations for a phenomenon

  9. According to the passage, one advantage of studying the

  isotope record of ocean sediments is that it

  (A) corresponds with the record of ice volume taken

  from rocks on land

  (B) shows little variation in isotope ratios when samples

  are taken from different continental locations

  (C) corresponds with predictions already made by

  climatologists and experts in other fields

  (D) confirms the record of ice volume initially

  established by analyzing variations in volcanic

  emissions

  (E) provides data that can be used to substantiate

  records concerning variations in the amount

  of sunlight received by the Earth

展开显示全文