GWD2的Q4求解

现在有一题语法题困扰我，请帮忙解答，谢啦

On earth, aomong the surest indication of sunspot cycles are believed to be the rate that tree grow, as seen in the rings visible in the cross sections of their trunks.

A. on earth, among the surest indication of sunspot cycles are believed to be the rate that trees grow

B.on earth, among the surest indication of sunspot cycles are, it is believed, the rate of trees growth

C.on earth, the rate at which trees grow is believed to 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

我认为答案是选E，可是答案是选C,请问选哪一个