A．They are not allowed to run on the road.

　　B．Their technical problems remain to be solved.

　　$来&源：gkxx.comC．They are now too expensive for consumers.

　　D．They are more dangerous for people on the street.

　　解析：选C。推理判断题。根据最后一段首句“Mason said the technology already works and the biggest challenge now is getting down the cost for driverless vehicles from hundreds of thousands of dollars to something more affordable.”可知，Mason曾说这种科技已经被运用了，但是最大的挑战就是把价格降下来，让人们更能支付得起。由此可判断，无人驾驶的最大的挑战就是价格太高。故选C。

　　Ⅱ.语法填空

　　阅读下面材料，在空白处填入适当的内容(1个单词)或括号内单词的正确形式。

　　A mother，wishing to encourage her son's progress in playing the piano，bought tickets to a performance by the great Polish pianist Ignace Jan Paderewski.1.

　　the evening arrived，they found their seats in the front of the concert hall and sat down.Soon 2.

　　mother found a friend to talk to，and the boy slipped away.

　　At eight o'clock，the lights in the auditorium began to dim 3.

　　the spotlights came on.4.

　　then did they notice the boy on the piano bench，innocently picking out “Twinkle，Twinkle，Little Star”．His mother gasped(喘息) in shock and 5.

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