马上要考了，请各位帮忙看看这个问题

abort

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

谁能告诉我这个as在这里是做什么用的？

遥远的绿洲

as指代前面主句

例:Although it claims to delve into political issues, television can be superficial, as when the three major networks each broadcast exactly the same statement from a political candidate.

abort

谢谢绿洲，但是这里我一直没搞明白，前面已经是主句了，而且有when作为连接，结构已经很清晰了，为什么还要as指代主句呢？

遥远的绿洲

我理解的也不透彻，可能属于语言的多样性吧，就是同一个意思可以用多种方式表达。中文里不是也有很多这样的例子吗？