[单项选择]About one million years ago, the Ice Age began. The Ice Age was a long period of time in which four great glaciers pushed southward to cover almost all the upper half of North America, and then melted away. Each glacier was a thick sheet of ice and snow that spread out from a centre near what is now Hudson Bay in Canada. The winters were long, and the cool summers were too short to melt much of the ice and snow. The ever-growing sheet built up to a thickness of two miles at its centre.
As all glaciers do, these great glaciers slid. They pushed down giant trees in their paths and scraped the earth bare of soil. Many animals moved farther south to escape. Others stayed and were destroyed.
When winters of little snow came, the summer sun cut into the edges of the ice sheets. As the glaciers melted, rocks, soil and other things that had mixed with the ice and snow were left. New hills, lakes and rivers were formed.
The last of the great glaciers began its melting about 11,00
A. 1,000 years
B. 100 years
C. 1,000,000 years
D. 11,000 years

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[单项选择]

As all glaciers do, these great glaciers slid. They pushed down giant trees in their paths and scraped the earth bare of soil. Many animals moved farther south to escape. Others stayed and were destroyed.
When winters of little snow came, the summer sun cut into the edges of the ice sheets. As the glaciers melted, rocks, soil and other things that had mixed with the ice and snow were left. New hills, lakes and rivers were formed.
The last of the great glaci
A. the Ice Age was a long period of time
B. great glaciers covered North America many years ago
C. changes in climate helped to melt the glaciers
D. how glaciers changed North America

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[单项选择]Passage Four

About one million years ago, the Ice Age began. The Ice Age was a long period of time in which four great glaciers pushed southward to cover almost all the upper half of North America, and then melted away. Each glacier was a thick sheet of ice and snow that spread out from a centre near what is now Hudson Bay in Canada. The winters were long, and the cool summers were too short to melt much of the ice and snow. The ever-growing sheet built up to a thickness of two miles at its centre.
As all glaciers do, these great glaciers slid. They pushed down giant trees in their paths and scraped the earth bare of soil. Many animals moved farther south to escape. Others stayed and were destroyed.
When winters of little snow came, the summer sun cut into the edges of the ice sheets. As the glaciers melted, rocks, soil and other things
A. the Ice Age was a long period of time
B. great glaciers covered North America many years ago
C. changes in climate helped to melt the glaciers
D. how glaciers changed North America

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[单项选择]

Ten thousand years ago, as the last ice age drew to a close, sea levels around the world were far lower than they are today. Much of the land under the North Sea and the English Channel was part of a huge region of forests and grassy plains. Then the climate gradually became warmer and the water trapped in glaciers and ice caps was released. This ancient land was submerged in the resulting deluge and all that remains to tell us that it was once lush and verdant— and inhabited — is the occasional stone tool, harpoon or mammoth tusk brought up from the sea bed by fishing boats.
Now the development of advanced sonar technology, known as bathymetry, is making it possible to study this flooded landscape in extraordinary detail. While previous devices have only been able to produce two-dimensional images, bathymetry makes use of computers, satellite positi
A. (A) It can attract more government funding for mapping.
B. (B) It only requires the use of an echo sounder.
C. (C) It can measure the depth of the sea bed with accuracy.
D. (D) It reveals important details of underwater topography.

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