如图，一个环形道，大圆半径为40米，小圆半径为30米，如果某人按大圆走一圈将比按小圆走一圈多走____米．

黄土高原“千沟万壑”的地貌特征主要是有下列哪种因素造成的（   ）

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D
    Hollywood's theory that machines with evil(邪恶) minds will drive armies of killer robots is just silly. The real problem relates to the possibility that artificial intelligence(AI) may become extremely good at achieving something other than what we really want. In 1960 a well-known mathematician Norbert Wiener, who founded the field of cybernetics（控制论）, put it this way: “If we use, to achieve our purposes, a mechanical agency with whose operation we cannot effectively interfere(干预), we had better be quite sure that the purpose which we really desire.”
    A machine with a specific purpose has another quality, one that we usually associate with living things: a wish to preserve its own existence. For the machine, this quality is not in-born, nor is it something introduced by humans; it is a logical consequence of the simple fact that the machine cannot achieve its original purpose if it is dead. So if we send out a robot with the single instruction of fetching coffee, it will have a strong desire to secure success by disabling its own off switch or even killing anyone who might interfere with its task. If we are not careful, then, we could face a kind of global chess match against very determined, super intelligent machines whose objectives conflict with our own, with the real world as the chessboard.
    The possibility of entering into and losing such a match should concentrate the minds of computer scientists. Some researchers argue that we can seal the machines inside a kind of firewall, using them to answer difficult questions but never allowing them to affect the real world. Unfortunately, that plan seems unlikely to work: we have yet to invent a firewall that is secure against ordinary humans, let alone super intelligent machines.
    Solving the safety problem well enough to move forward in AI seems to be possible but not easy. There are probably decades in which to plan for the arrival of super intelligent machines. But the problem should not be dismissed out of hand, as it has been by some AI researchers. Some argue that humans and machines can coexist as long as they work in teams—yet that is not possible unless machines share the goals of humans. Others say we can just “switch them off” as if super intelligent machines are too stupid to think of that possibility. Still others think that super intelligent AI will never happen. On September 11, 1933, famous physicist Ernest Rutherford stated, with confidence, “Anyone who expects a source of power in the transformation of these atoms is talking moonshine.” However, on September 12, 1933, physicist Leo Szilard invented the neutron-induced(中子诱导) nuclear chain reaction.

下列各句中，划线的成语使用正确的一句是（）

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    A small boy at summer camp received a large package of cookies (饼干) in the mail from his mother. He ate a few, and then 1 the rest under his bed. The next day, after lunch, he went to his tent to get a cookie. The box was2

That afternoon a camp teacher, who had been 3of the theft (失窃), saw another boy sitting behind a tree eating the stolen 4 “That young man,” he said to himself, “must be taught not to 5”

    He returned to the group and met the boy 6 cookies had been stolen. Billy, he said, “I know who stole your cookies. Will you 7 me teach him a lesson?”

    “Well, yes —8aren’t you going to punish him?” asked the puzzled boy.

    “No, that would only make him 9 you,” the teacher explained. “I want you to call your 10and ask her to send you another box of cookies.”

    The boy did 11the teacher asked and a few days 12 received another box of cookies in the mail.

    “Now,” said the teacher, ‘“the boy who stole your cookies is down by the lake.” Go down there and13your cookies with him.

    “But,” protested (抗议) the boy, “he’s the14”

    “I know. But 15 it - see what happens.”

    Half an hour later the camp teacher saw the two come up the hill,16 The boy who had stolen the cookies was 17 to get the other to accept his jackknife (折叠小刀) in18for the stolen cookies, and the victim was just 19the gift from his new friend, saying that a few old cookies weren’t that 20 anyway.