Careful observations and systematic studies of sunspots If an intense sunspot activity had occurred in 1857, the next one would

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问题 Careful observations and systematic studies of sunspots
If an intense sunspot activity had occurred in 1857, the next one would have been in

选项 A、1858.
B、1862.
C、1865.
D、1868.

答案D

解析 答案在本文第四段的第三句话。太阳黑子的剧烈活动每十一年爆发一次,因此如果上一次发生在1857年,那么下一次就会发生在1868年。
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