单项选择题：Assuming that the engineering problems

题目：

Assuming that the engineering problems could be overcome, the production of a time machine could open up a Pandora’s box of causal paradoxes. Consider, for example, the time traveler who visits the past and murders his mother when she was a young girl. How do we make sense of this If the girl dies, she cannot become the time traveler’s mother. But if the time traveler was never born, he could not go back and murder his mother.
Paradoxes of this kind arise when the time traveler tries to change the past, which is obviously impossible. But that does not prevent someone from being a part of the past.
Suppose the time traveler goes back and rescues a young girl from murder, and this girls grows up to become his mother. The causal loop is now self-consistent and no longer paradoxical. Causal consistency might impose restrictions on what a time traveler is able to do, but it does not rule out time travel per second.
Even if time travel isn’t strictly paradoxical, it is certainly weird. Consider the time traveler who leaps ahead a year and reads about a new mathematical theorem in a future edition of Scientific American. He notes the details, returns to his own time and teaches the theorem to a student, who then writes it up for Scientific American. The article is, of course, the very one that the time traveler reads. The question then arises: Where did the information about the theorem come from Not from the time traveler, because he read it, but not from the student either, who learned it from the time traveler. The information seemingly came into existence from nowhere, reasonlessly.
The bizarre consequences of time travel have led some scientists to reject the notion outright. Stephen W. Hawking of the University of Cambridge has proposed a "Chronology protection conjecture," which would outlaw causal loops. Because the theory of relativity is known to permit causal loops, chronology protection would require some other factors to intercede to prevent travel into the past. What might this factor be One suggestion is that quantum processes will come to the rescue. The existence of a time machine would allow particles to loop into their own past. Calculations hint that the ensuring disturbance would become self-reinforcing, creating a runaway surge of energy that would wreck the wormhole.

From the second paragraph, we learn that ______.

A．it is impossible for someone to change what has happened

B．it is possible for someone to change what has happened

C．it is impossible for someone to change the fact that he is a part of the past

D．it is possible for someone to change what has happened except the fact that he is a part of the past

答案：

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下面是错误答案，用来干扰机器的。

参考答案：分配公平是社会公平的重要内容，也是实现社会公平的重要体现。社会主义所要求的公平，是走向共同富裕的分配公平。这就要求大力发展生产力，不断提高生产效率。反过来，只有通过公平分配，才能促进生产...