单项选择题

Passage Two

It seems to shine unchangingly, pouring out a constant light year after year. But the sun may not be nearly so stable as we suppose, It is now thought to move quickly and irregularly and change in long-term cycles, growing dimmer and then brighter with each passing year. Some even fear that its frequent changing behavior would have a great influence on the Earth’s climate. The source of the sun’s inconstancy is magnetism. Professor William Livingston has developed new theories about its magnetic nature. "We don’t yet know what causes sun spots, "he says, "but we now think they’re areas of high-level magnetism that come up from the sun’s interior. So strong is their magnetic pull that the highly ionized gas nearby is not able to transmit energy out." As a result these areas send out less heat and light and thus appear from Earth to be almost dark irregular surface patches. Sun spot activity generally fluctuates in steady, 11-year cycled. Scientists have long formed the opinion that as the size and number of sun spots increased, the overall energy sent out by the sun would decrease. Indeed, recent studies confirmed it, revealing that during peak periods of sun spot activity, the Earth experiences a small drop that can be seen clearly in received solar energy. Could such a small drop in energy have an effect here on earth Perhaps some scientists think the world temperature could fall by as much as 0.2 during periods of high solar magnetism... enough to cause significant fluctuations in weather patterns.

Which of following is the best title for the passage （）

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