What is the main idea of this passage？A．The Ice Age was a long period of time.B．Great glac
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What is the main idea of this passage？
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.
请帮忙给出正确答案和分析，谢谢！
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正确答案：D
主旨题。对于这类问题应十分关注首尾句。文章开篇讲到冰河时期里4块巨大的冰川向南移动覆盖了北美洲的上半部。之后文章主要讲述冰川移动和融化过程中对北美洲产生的影响。故选项D正确。