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　　Passage 4

　　Volcanoes （火山） have been erupting （爆发） on the earth for millions of years. More than five hundred still erupt today. These are called active volcanoes. Volcanoes are located in belts or chains. They are found where the earth's crust （外壳） is weak. The weak spots let the hot rock escape when the volcano erupts.

　　Many volcano belts are mountain ranges along the edges of continents. One belt runs along the western coast of South America up through the western part of the United States. Other volcanoes are found in ocean basins.

　　About three-fifths of all active volcanoes in the world are in the Pacific Ocean. Many of these volcanoes erupt under the water. The Hawaiian Islands were built by volcanoes that began erupting under water and finally reached the surface of the ocean.

　　1. The selection says that about five hundred volcanoes ______.

　　A. will erupt this year B. are still active C. are located under water

　　D. are all that have ever been discovered 首段首句非常关键 1. B

　　2. Volcanoes are found ______.

　　A. where the earth's crust is weak B. along the edges of continents C. in the ocean basins of the world

　　D. all of the above 2. D

　　3. Most of the active volcanoes are located in ______.

　　A. South America B. the Pacific Ocean C. the western United States D. the Atlantic Ocean

　　3. B

　　4. The Hawaiian Islands were built by volcanoes that ______.

　　A. began erupting under water

　　B. formed a mountain range under water

　　C. finally reached the surface of the ocean

　　D. Both A and C

　　4. D

　　5. The best title for this selection is ______.

　　A. How the Hawaiian Islands Were Built

　　B. At the Bottom of the Ocean

　　C. Why Volcanoes Erupt

　　D. The Earth's Volcanoes

　　5. D