Paragraph 2 
After the Second World War, the use of sonar revolutionized surveys of the sea 
floor, making accurate mapping of the ocean basins possible. Far from finding merely 
the flat plains previously imagined, scientists discovered gigantic mountain ranges, 
isolated seamounts, and deep trenches. The mid-ocean ridge is by far the largest 
geological feature on Earth, but it had remained unknown and hidden from human 
observation except for what are in fact glimpses of its mountains that here and there 
break the sea’s surface as islands. It was the mapping of a great mid-ocean mountain 
range that, incredibly, extends through all the ocean basins that was the key to 
understanding continental drift. 
4.Which of the sentences below best expresses the essential information in the 
highlighted sentence in the passage? In correct choices change the meaning in 
important ways or leave out essential information. 
A.Earth’s largest geological feature remained hidden until it was glimpsed, here and 
there, beneath the oceans’ islands. 
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内部资料泄露必究
B.The mid-ocean mountain range, Earth’s largest geological feature, was 
undiscovered because it is visible only where its peaks appear above the sea 
surface as islands. 
C.The mid-ocean ridge remains unobservable except for brief periods of time when 
mountains can be glimpsed above the sea’s surface. 
D.It is now known that Earth’s islands are in fact created when the mid-ocean 
mountain range is so high that it breaks the sea’s surface. 
Paragraph 3 
As geologists began to investigate part of the range that extends up the Atlantic 
(the Mid-Atlantic Ridge), they found evidence that the ocean floor was spreading 
apart, thus supporting Wegener’s idea of continental drift. Rocks near the center of the 
ridge were younger than those further away. Moreover, the further away from the 
ridge the geologists looked, the more overlying sediment there was, suggesting the 
rocks beneath had been there longer. The final piece of evidence came when the 
magnetism of the rocks was examined. Every so often, in geological time, Earth’s 
magnetic field reverses its polarity so that the magnetic north switches to the south. 
Magnetic particles in molten rock align themselves to the new direction. Geologists 
found a series of bands or strips of alternating magnetic polarity in the rocks of the 
Mid-Atlantic Ridge, each one signifying a change in Earth’s polarity. These bands run 
parallel to each other along the length of the ridge. They also discovered that the 
series of bands on either side of the ridge are mirror images of each other. Here, then, 
was the evidence that continents were moving apart. Wegener’s theory was accepted. 
5.According to paragraph 3, all of the following provided geologists with essential 
evidence about the widening of the ocean floor in the Atlantic Ocean EXCEPT: 
A.Measurements showing an increase in the distance between the continents on 
either side of the Atlantic Ocean 
B.The comparatively young age of rocks close to the Mid-Atlantic Ridge 
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内部资料泄露必究
C.The increase in sediment with increasing distance from the Mid-Atlantic Ridge 
D.The periodic reversal of the magnetic polarity of rocks on the Atlantic sea floor 
Paragraph 4 
It is now recognized that the surface of Earth is divided into 13 major plates and 
a number of smaller ones. The undersea mountain ranges are along edges of these 
plates. The plates float on top of the partially molten layer of the mantle, which is the 
inner part of the planet between the rocky outer part (the lithosphere) and the core. 
Some of these plates carry continents, but others are purely oceanic. Those that do 
carry continents are responsible for continental drift. Continents move at the same rate 
as the plates are moving apart or together—2 centimeters per year in the Atlantic and 
18 centimeters per year in the eastern Pacific. It is thought that currents within the 
fluid rock of the mantle below cause the plates to move. The plates, which are 
50—100 kilometers thick, consist of the surface crust of Earth and a part of the upper 
mantle, both of which are rock. The crust part varies in nature. Continental crust, or 
land, is thicker (30—40km) but less dense than oceanic crust (only 6 km). This 
difference in density accounts for the oceans themselves. Despite being thinner, the 
denser oceanic crust floats lower in the liquid rock of the mantle than the lighter 
continental crust. Water flows by gravity to the lower areas, thus creating the oceans. 
6.Which of the following facts about the ocean is directly explained in paragraph 4? 
A.Why oceans cover a larger area of Earth’s surface than continental crust does 
B.Why oceanic crust is denser than continental crust 
C.Why oceans form where they do 
D.Why oceanic crust is thinner than continental crust 
7.Paragraph 4 supports which TWO of the following statements about differences 
between oceanic crust and continental crust? To receive credit, you must select 
TWO answers. 
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内部资料泄露必究
A.Oceanic crust is denser than continental crust. 
B.Oceanic crust is not as thick as continental crust. 
C.Oceanic crust contains part of the upper mantle but continental crust does not. 
D.Oceanic crust floats in liquid rock but continental crust does not. 
8.Which of the following questions is NOT answered by paragraph 4? 
A.Where is the lithosphere located in relationship to the other layers of Earth? 
B.How is it possible for the speed of currents within the fluid rock of the mantle to 
vary from one location to another? 
C.Which type of plate is responsible for continental drift? 
D.How many major plates make up the surface of Earth? 
9.Look at the four squares [◼] that indicate where the following sentence could be 
added to the passage.
For example, the age of seafloor rock varied in relation to its distance from 
the ridge. 
Where would the sentence best fit? Click on a square [◼] to add the sentence to the 
passage. 
As geologists began to investigate part of the range that extends up the Atlantic 
(the Mid-Atlantic Ridge), they found evidence that the ocean floor was spreading 
apart, thus supporting Wegener’s idea of continental drift. ◼ Rocks near the center of 
the ridge were younger than those further away. Moreover, the further away from the 
ridge the geologists looked, the more overlying sediment there was, suggesting the 
rocks beneath had been there longer. ◼ The final piece of evidence came when the 
magnetism of the rocks was examined. Every so often, in geological time, Earth’s 
magnetic field reverses its polarity so that the magnetic north switches to the south. 
Magnetic particles in molten rock align themselves to the new direction. ◼ Geologists 
25 
 

内部资料泄露必究
found a series of bands or strips of alternating magnetic polarity in the rocks of the 
Mid-Atlantic Ridge, each one signifying a change in Earth’s polarity. These bands run 
parallel to each other along the length of the ridge. They also discovered that the 
series of bands on either side of the ridge are mirror images of each other. ◼ Here, 
then, was the evidence that continents were moving apart. Wegener’s theory was 
accepted.