问题补充：
About one million years ago,the Ice Age began.The Ice Age was a long period of time in which four great glaciers(冰川) 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 center 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 evergrowing sheet built up to a thickness of two miles at its center.
As all glaciers do,these great glaciers slid(滑动). They pushed down giant trees in their paths and scraped(刮削)the earth bare(光秃秃)of soil.Many animals moved farther south to escape.Others stayed and were destroyed.
When winters of little snow came,the summer suns into the edges to 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 11 000 years ago.Itsmelting formed the Great Lakes.These lakes are today little changed from their early sizes the glaciers.This is the Mississippi Missouri Ohio system.These rivers were miles wide at first.Through the years they settle into their present channels.
The main idea of this passage is .
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
2.The author states that all glaciers .
A.are two miles thick B.form frozen lakes
C.are a million years old D.move and slide
3.From the information in this passage we know that .
A.glaciers are destructive
B.all glaciers in the world move southward
C.the Mississippi Missouri Ohio systems is larger than it was before the Ice Age
D.the Great Lakes are now smaller than they were before the Ice Age
4.The Ice Age lasted almost .
A.1 000 years B.100 years C.1 000 000 years D.11 000 years
5.In the last sentence,the word “their” refers to .
A.lakes B.rivers C.glaciers D.systems 1----5 DDACB
答案：
(答案→)1----5 DDACB
解析：
1.这是一】阅读理解第一段叙述四大冰川覆盖了北美的北部地区；中间两段主要叙述了冰川的变化及对土地的改变；最后一段说明了北美的一些地形是由于冰川造成的。所以答案为冰川怎样改变了北美。答案为D。
2.这是一道推断题。尽管作者写了冰川存在的时间、厚度，然而，主旨是写冰川对地形的改变，而造成这种地形改变的原因是冰川的滑动。答案为D。
3.这是一道主旨题。从第二、三段可以知道冰川是具有破坏性的，带走土壤和树木，迫使动
物迁移；B选项中的“all”带有绝对性，文中作者并未如此表述；C选项与最后一段的倒数第二句话相矛盾；D选项中提到的“Great Lakes”在最后一段的第二、三句中说明Ice Age 前
后他们的大小并未作很大的改变。答案为A。
4.这是一道计算题。第一句话“About one million years ago,the Ice Age began.”告诉
我们Ice Age延续的时间大约为一百万年。答案为C。
5.这是一道所指题。最后两句话“These rivers were miles wide at first.Through the years they settle into their present channels.”说明“their”指的是rivers，而不是指lakes。答案为B。
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