The failed Skylab will come screaming home to earth in disappointment sometime next month. But it will fall we know not where.
　　That precise information is beyond even the calculations of scientists and their computers.
　　The best they can tell us is that the space station, weighing 77 tons and as high as a 12 story building, will break into hundreds of pieces that will be scattered across a track 100 miles wide and 4,000 miles long.
　　We are again exposed to one of those unexpected adventures, or misadventures, of science that attracts our attention from the boring routines of daily existence and encourages us to think a lot about man’s future.
　　What worries Richard Smith, the Skylab’s director, is the “big pieces” that will come through the atmosphere, Two lumps, weighing 2 tons each, and ten, weighing at least 1,000 pounds each, will come in at speeds of hundreds of miles an hour and if they crash on land they will dig holes up to 100 feet deep.
　　What worries us, with our lack of scientific knowledge and our quick imagination, is both the big and little pieces, although project officials say there is a very small chance that anyone will be injured by them.
　　That’s good to know, but it doesn’t remove the doubts of the millions who still remember the nuclear accident at Three Mile Island. That accident took place in 1979 in spite of what the officials had assured us as to the safely of the nuclear reactor.

　　21. Where the Skylab will fall?
　　A) is kept secret
　　B) has been made public
　　C) has been predicted by scientists
　　D) can’t be predicted even by computers（D）

　　22. According to the passage, what does an incident such as the failed Skylab lead us to do?
　　A) Not to believe in officials.
　　B) To think about our future.
　　C) Has been predicted by scientists.
　　D) To fear for our lives.（D）

　　23. The author suggests that ________.
　　A) the danger of the Skylab’s fall has been overestimated
　　B) it’s useless to worry over things you can’t do anything about
　　C) the danger of the Skylab’s fall has been underestimated
　　D) computers can solve the problem caused by the broken Skylab（A）

　　24. The author refers to Three Mils Island ________.
　　A) because he is doubtful about what the officials said
　　B) because he fears that a piece of the Skylab may strike a nuclear power plant
　　C) because he is afraid of the use of nuclear power
　　D) because the nuclear reactor there and the Skylab were both built by the same company（B）

　　25. This passage is mainly about the author’s ________.
　　A) interest in the failure of the Skylab
　　B) willingness to give his advice
　　C) eagerness to see more new scientific discoveries
　　D) concern that science cannot answer all questions（C）