多选题 Directions: The passage below is followed by questions based on its content. Once you have read the passage, select the answer choice that best answers each question. Answer all questions on the basis of what is stated or implied in the passage.
For each of Questions 15-20, select one answer choice unless otherwise instructed.
Questions 15-17 are based on the following passage. (The passage was written in the latter half of the 20th century.)
The coastlines on the two sides of the
Atlantic Ocean present a notable parallelism:
the easternmost region of Brazil, in
Line Pernambuco, has a convexity that corre-
(5) sponds almost perfectly with the concavity of
the African Gulf of Guinea, while the con-
tours of the African coastline between Rio de
Oro and Liberia would, by the same approx-
imation, match those of the Caribbean Sea.
(10) Similar correspondences are also observed
in many other regions of the Earth. This
observation began to awaken scientific inter-
est about sixty years ago, when Alfred
Wegener, a professor at the University of
(15) Hamburg, used it as a basis for formulating a
revolutionary theory in geological science.
According to Wegener, there was origi-
nally only one continent or land mass, which
he called Pangaea. Inasmuch as continental
(20) masses are lighter than the base on which
they rest, he reasoned, they must float on the
substratum of igneous rock, known as sima,
as ice floes float on the sea. Then why, he
asked, might continents not be subject to
(25) drifting? The rotation of the globe and other
forces, he thought, had caused the cracking
and, finally, the breaking apart of the origi-
nal Pangaea, along an extensive line repre-
sented today by the longitudinal submerged
(30) mountain range in the center of the Atlantic.
While Africa seems to have remained static,
the Americas apparently drifted toward the
west until they reached their present position
after more than 100 million years. Although
(35) the phenomenon seems fantastic, accus-
tomed as we are to the concept of the rigid-
ity and immobility of the continents, on the
basis of the distance that separates them it is
possible to calculate that the continental
(40) drift would have been no greater than two
inches per year.
单选题 The primary purpose of the passage is to
  • A. describe the relative speed of continental movement
  • B. predict the future configuration of the continents
  • C. refute a radical theory postulating continental movement
  • D. describe the reasoning behind a geological theory
  • E. explain how to calculate the continental drift per year
【正确答案】 D
【答案解析】The author takes the reader through Wegener's reasoning step by step, describing what led Wegener to reach his conclusions.
单选题 It can be inferred from the passage that evidence for continental drift has been provided by the
  • A. correspondences between coastal contours
  • B. proof of an original solitary land mass
  • C. level of sima underlying the continents
  • D. immobility of the African continent
  • E. relative heaviness of the continental masses
【正确答案】 A
【答案解析】Since the existence of the correspondences between the various coastal contours was used by Wegener as a basis for formulating his theory of continental drift, it can be inferred that the correspondences provide evidence for the theory. Choice B is incorrect. The passage does not indicate that Pangaea's existence has been proved. Choice C is incorrect. It is the relative heaviness of sima, not the level or depth of sima, that suggested the possibility of the lighter continents drifting. Choice D is incorrect. Mobility rather than immobility would provide evidence for continental drift. Choice E is incorrect. The continents are lighter than the underlying sima.
单选题 The passage presents information that would answer which of the following questions?
  • A. In what ways do the coastlines of Africa and South America differ from one another?
  • B. How much lighter than the substratum of igneous rock below them are the continental masses?
  • C. Is the rotation of the globe affecting the stability of the present day continental masses?
  • D. According to Wegener's theory, in what direction have the Americas tended to move?
  • E. How does Wegener's theory account for the apparent immobility of the African continent?
【正确答案】 D
【答案解析】Choice D is answerable on the basis of the passage. The next-to-the-last sentence of the second paragraph states that the Americas "apparently drifted toward the west."