题目

 完形填空Joe wants a computer. He asks his parents for the money but they say he must get it himself. But how does he get it? He   1   about this when he walks home. Not many people want to ask children to work for them. Maybe he can take away snow for the neighbors. But it is not ___2___. He has to __3__ a long time for that. He can' t cut grass for their gardens   4   he has no tools to do the work. Then he    5   one of his classmates, Dick. He is delivering(送)   ___6___. “I can do that”, he thinks, “Maybe I can even get the computer right away. I can ___7__ for 棱台的三视图与直观图如图所示.（1）求证：平面平面；（2）在线段上是否存在一点，使与平面所成的角的正弦值为？若存在，指出点的位置；若不存在，说明理由.