When the glaciers（ ）after the last ice age,the five Great Lakes of North America were formed.

单选题

When the glaciers（ ）after the last ice age,the five Great Lakes of North America were formed.

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材料题

directions and at different speeds. By mapping the same ice caps now, in winter, when the surface remains frozen all day, and then comparing the winter and summer velocities, the researchers will be able to isolate the effects of melt water.Above is a view of a small part of the Hofsjkull ice cap, which encompasses several glaciers. The fan at upper left is part of a glacier called Mlaj?kull.For more on the research, see this NASA press release.What is the mission of the NASA radar instrument?

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材料题

s and at different speeds. By mapping the same ice caps now, in winter, when the surface remains frozen all day, and then comparing the winter and summer velocities, the researchers will be able to isolate the effects of melt water.Above is a view of a small part of the Hofsjkull ice cap, which encompasses several glaciers. The fan at upper left is part of a glacier called Mlaj?kull.For more on the research, see this NASA press release.What does the underlined word permanent （paragragh 2） mean?

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单选题

In the heart of Patagonia area, glaciers rise in the midst of mountain capes and alpine meadows, close enough to hike right up to and （ ）.

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单选题

When the spring compresses, the valve opens.

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