Geologists(地質學家)have been studying volcanoes for a long time. Though they have learned a great deal, they still have not discovered the causes of volcanic action. They know that the inside of the earth is very hot, but they are not sure exactly what causes the great heat. Some geologists have thought that the heat is caused by the great pressure of the earth’s outer layers. Or the heat may be left from the time when the earth was formed. During the last sixty years scientists have learned about radium, uranium, thorium, and other radioactive elements. These give out heat all the time as they change into other elements. Many scientists now believe that much of the heat inside the earth is produced by radioactive elements.

　　Whatever the cause of the heat may be, we do know that the earth gets hotter the farther down we dig. In deep mines and oil wells the temperature rises about 1℉ for each 50 feet. At this rate the temperature 40 miles below the earth’s surface would be over 4000℉ . this is much hotter than necessary to melt rook. However, the pressure of the rock above keeps most materials from melting at their usual melting points. Geologists believe that the rock deep in the earth may be plastic, or puttylike(似粘性材料). In other words, the rock yields slowly to pressure nut is not liquid. But if some change in the earth’s crust releases the pressure, the rock melts. Then the hot, liquid rock can move up toward the surface.

　　Where the melted rock works its way closed to the earth’s crust, a volcano may be formed. The melted rock often contains steam and other gases under great pressure. If the rock above gives way, the pressure is released. Then the sudden expansion of the gases causes explosions. These blow the melted rock into pieces of different sizes and shoot them high in the air. Here they cool and harden into volcanic ash and cinders(灰燼). Some of this material falls around the hole made in the earth’s surface. The melted rock may keep on rising and pour out as lava(巖漿). In this way, volcanic ash, cinders, and lava build up the cone-shaped(錐形的)mountains that we call volcanoes.

　　64. The subject of this passage is the ____.

　　A. formation of volcanoes B. results of volcanic action

　　C. interior of the earth D. causes of the earth’s internal heat

　　65. The cause for the heat in the interior of the earth is probably ____.

　　A. radioactive elements B. the great pressure of the earth

　　C. not determined D. the heat remaining from the formation of the earth

　　66. From the information given in the passage, most minerals would melt fastest ____.

　　A. at 4000 ℉ at sea level B. at 4000 ℉, 5000 feet below sea level

　　C. in the absence of oxygen D. at the exact center of the earth at 4000℉

　　67. If the temperature at the earth’s surface is 20℉ the temperature in a coal mine 500 feet below the surface would, in degrees, be ____.

　　A. 40 B. 30 C. 50 D. 120

　　D

　　Thirty-two people watched Kitty Genovese being killed right beneath their windows. She was their neighbor. Yet none of the 32 helped her. No one even called the police. Was this in gunman cruelty? Was it lack of feeling about one’s fellow man?

　　“Not so,” say scientists John Barley and Bib Fatane. These men went beyond the headlines to probe the reasons why people didn’t act. They found that a person has to go through two steps before he can help. First he has to notice that is an emergency.

　　Suppose you see a middle-aged man fall to the sidewalk. Is he having a heart attack? Is he in a coma(昏迷)from diabetes(糖尿病)? Or is he about to sleep off a drunk?

　　Is the smoking coming into the room from a leak in the air conditioning? Is it “steam pipes”? or is it really smoke from a fire? It’s not always easy to tell if you are facing a real emergency.