脊线（Ridge lines）

A.正脊，垂脊

B.正脊，戗脊

C.主脊，垂脊

D.N/A

A．To argue that wind farms should not be built along ridge lines

B．¨To point out that the deaths of migratory birds exceed the deaths of birds of prey

C．¨To explain why some environmentalists oppose wind energy

D．¨To suggest that wind turbines result in relatively few bird deaths

A．To argue that wind farms should not be built along ridge lines

B．¨To point out that the deaths of migratory birds exceed the deaths of birds of prey

C．¨To explain why some environmentalists oppose wind energy

D．¨To suggest that wind turbines result in relatively few bird deaths

differences that themselves depend on the position of the continents. Such a back-coupling, in which the position of the moving plate has an impact on the forces that move it, could produce complicated and varying motions.

On the other hand, the theory is implausible because convection does not normally occur along lines, and it certainly does not occur along lines broken by frequent offsets or changes in direction, as the ridge is. Also it is difficult to see how the theory applies to the plate between the Mid-Atlantic Ridge and the ridge in the Indian Ocean. This plate is growing on both sides, and since there is no intermediate trench, the two ridges must be moving apart. It would be odd if the rising convection currents kept exact pace with them. An alternative theory is that the sinking part of the plate, which is denser than the hotter surrounding mantle, pulls the rest of the plate after it. Again it is difficult to see how this applies to the ridge in the South Atlantic, where neither the African nor the American plate has a sinking part.

Another possibility is that the sinking plate cools the neighboring mantle and produces convection currents that move the plates. This last theory is attractive because it gives some hope of explaining the enclosed seas, such as the Sea of Japan. These seas have a typical oceanic floor, except that the floor is overlaid by several kilometers of sediment. Their floors have probably been sinking for long periods.

It seems possible that a sinking current of cooled mantle material on the upper side of the plate might be the cause of such deep basins. The enclosed seas are an important feature of the earth's surface and seriously require explanation because, in addition to the enclosed seas that are developing at present behind island arcs, there are a number of older ones of possibly similar origin, such as the Gulf of Mexico, the Black Sea, and perhaps the North Sea.

According to the traditional view of the origin of the ocean basins, which of the following is sufficient to move the continental plates？ ______

A．Increases in sedimentation on ocean floors.

B．Movement of mid-ocean ridges.

C．Sinking of ocean basins.

D．Differences in temperature under oceans and continents.

Section B

Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice.

No very satisfactory account of the mechanism that caused the formation of the ocean basins has yet been given. The traditional view supposes that the upper layer of the earth behaves as a liquid when it is subjected to small focus for long periods and that differences in temperature under oceans and continents are sufficient to produce movements in the upper layer of the earth with rising currents under the mid- ocean ridges (山脊) and sinking currents under the continents. Theoretically, these movements would carry the continental plates along as though they were on a conveyor belt and would provide the forces needed to produce the split that occur along the ridge. This view may be correct. It has the advantage that the currents are driven by temperature differences that themselves depend on the position of the continents.

On the other hand, the theory is unconvincing because the movements do not normally occur along lines, and it certainly does not occur along lines broken by frequent changes in direction, as the ridge is. Also, it is difficult to see how the theory applies to the plate between the Mid-Atlantic Ridge and the ridge in the Indian Ocean. This plate is growing on both sides, and since there is no intermediate trench, the two ridges must be moving apart. An alternative theory is that the sinking part of the plate, which is denser than the hotter surroundings, pulls the rest of plate after it. Again it is difficult to see how this applies to the ridge in the South Atlantic, where neither the African nor the American plate has a sinking part.

Another possibility is that the sinking plate cools the neighboring mantle (地幔) and produces motion currents that move the plates. This last theory is attractive because it gives some hope of explaining the neighboring mantle and produces motion currents that move the plates. This last theory is attractive because it gives some hope of explaining the enclosed seas. These seas have a typical oceanic floor, except that the floor is overlaid by several kilometers of sediment (沉积物). Their floors have probably been sinking for long periods. It seems possible that a sinking current of cooled material on the upper side of the might be the cause of such deep basins. The enclosed seas are an important feature of the earth's surface and seriously require explanation.

Which of the following titles would best describe the content of the text？

A．Several Theories of Ocean Basin Formation.

B．The Traditional View of the Oceans.

C．Temperature Differences Among the Oceans.

D．Motions and Ocean Currents.

等价值线(isovalue lines)

A.256 address lines 256根地址线

B.6 address lines 6根地址线

C.1 address line 1根地址线

D.8 address lines 8根地址线

等价值线（iso value lines) 名词解释

图中俯视图的相贯线是正确的。 According to the given drawings, the interesection lines in the top view are right.