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 [单项选择]Just 30 years ago some 700 million people lived in cities. Today the number (1) at 1,800 million, and by the end of the century it will be up to 3,000 million—more than half the world’s (2) population. By the year 2000, it is said 650 million people will (3) into 60 cities of five million or more—three quarters of them in the (4) world. Only a single First World city—metropolitan Tokyo, which will have 24 million people—is (5) to be among the global top five; London, (6) second in 1950 with ten million people, will not (7) make 2000’s top 25. In places (8) rates of natural population increase (9) three percent annually—meaning much of the Third World—that (10) is enough to double a city’s population within 20 years. But (11) powerful are the streams of hopeful (12) from the countryside.
What faces and confuses urban planners is the huge scale of these (13) . Ther A. solitary B. alone C. lonely D. isolated 我来回答: 提交
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