Prep sc1-139. 好难啊，全倒装

139.
                (32262-!-item-!-188;#058&006043)

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.

(A) On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow

(B) On Earth, among the surest indications of sunspot cycles are, it is believed, the rate of tree growth

(C) On Earth, the rate at which trees grow is believed to be among the surest indications of sunspot cycles

(D) Among the surest indications on Earth of sunspot cycles, believed to be the tree growth rate

(E) Among the surest indications on Earth of sunspot cycles is believed to be the rate at which trees grow

答案是E. 句子是全倒装，那么C为什么不对？这里有必要一定倒装吗？