prep 59关于指代

59. 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

请问c,和e表达上的区别？

还有they为什么在e中就指代没有歧义，在c就不行了呢？

有什么顺序么？我只知道应该优先指代主语。。。。显然在这里判断时候没用。。。

LZ MM还没考滴～ MM

C里面的on earth是修饰整个句子的，在地球上，the rate at which trees grow is believed to be among...
暗含在别的星球上the rate at which trees grow 是不是 believed to be among...就不知道了

E里面的on earth是修饰 the surest indications of sunspot cycles 的，在地球上的indication，这个意义比较合理

个人感觉，请大家批评指正～ 

选项里没THEY啊

不过ON EARTH有究竟的意思哦，是副词，放在句首可能有歧义

如果在句中就是介词

是个全倒结构

这个解释合理，可是有NN说是指代问题，我就不明白了。。。哎。。。本来指代就不明白：

NN说：

A: among倒装，主语应该是the rate所以用单数is

B: 同上

C: their的指代存在歧义，离它最近的是sunspot cycles

D: believed应该用被动

E: correct

我很弱的，你看我问题多多阿。。。。下周就考还这样。。。太伤心了