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题库 / Prep2007E1-SC-139
On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow, as seen in the rings visible in the cross sections of their trunks.
On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow
On Earth, among the surest indications of sunspot cycles are, it is believed, the rate of tree growth
On Earth, the rate at which trees grow is believed to be among the surest indications of sunspot cycles
Among the surest indications on Earth of sunspot cycles, believed to be the tree growth rate
Among the surest indications on Earth of sunspot cycles is believed to be the rate at which trees grow
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老师，我可以排除A，B因为are，可以排除D因为不是一个完整句子，但不明白C错在哪里，谢谢了。
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