下列办法中能改变通电螺线管磁性强弱的是(     )

①2H ②2NH₃ ③SO₂ ④ $\stackrel{+2}{Cu}$ O ⑤Mg²⁺ ⑥2OH^﹣ ⑦H₂O．

    In 1863, the great novelist Jules Verne wrote a novel called Paris in the Twentieth Century. In the book he used the full power of his great ability to forecast the coming century. Unfortunately, the manuscript (手稿) was lost until his great-grandson happened to discover it lying in a safe where it had been carefully locked away for almost 130 years. Realizing what a treasure he had found, he arranged to have it published in 1994, and it became a bestseller at once.

    Back in 1863, kings still ruled the ancient world in Europe, with so many poor people working in the fields. And steam power was just beginning to change the world. But Verne predicted that Paris in 1960 would have glass skyscrapers, air conditioning, TV, high-speed trains, gas-powered vehicles, and even something similar to the Internet. Verne described life in modem Paris almost without any mistakes.

    Just two years later Verne made another amazing prediction. He wrote From the Earth to the Moon, in which he predicted the details of the task that sent several astronauts to the moon 100 years later in 1969. He correctly predicted the size of the space capsule, the number of astronauts who would carry out the task, the weightlessness that the astronauts would experience, and the final landing in the ocean.

    How was Jules Verne able to predict 100 years into the future successfully? Although he was not a scientist himself, Verne often turned to scientists, asking them questions about their opinions of the future. He collected a vast amount of information about the great scientific discoveries of his time. Verne realized that science would make it possible for many amazing things to appear in the future. The secret of his successful prediction was his belief in the power of science to change society.

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