又有一道PREP和GWD答案不同的SC

Q26:

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.

1. On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow
2. On Earth, among the surest indications of sunspot cycles are, it is believed, the rate of tree growth
3. On Earth, the rate at which trees grow is believed to be among the surest indications of sunspot cycles
4. Among the surest indications on Earth of sunspot cycles, believed to be the tree growth rate
5. Among the surest indications on Earth of sunspot cycles is believed to be the rate at which trees grow

GWD上的答案是C，我也倾向C，不过PREP SC语法总结上选的是E。还是有点不明白，请NN指教，谢谢！

C 有两个问题：

1# on earth 修饰的是Among the surest indications ， C 离的太远，容易有歧义

2# 后面未划线部分as seen in the rings visible in the cross sections of their trunks. 要比较的是the rate at which trees grow， C 同样把比较对象分割太远。

Open to discuss..........