Prep-1-139 求助

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.

句子结构是什么? 不明白.

同问这里句尾as的用法？

还有另外一题Prep-1-132：

A recent review of pay scales indicates that CEO’s now earn an average of 419 times more pay than blue-collar workers, compared to a ratio of 42 times in 1980.

     A     that CEO’s now earn an average of 419 times more pay than blue-collar workers, compared to a ratio of 42 times

     A     that CEO’s now earn an average of 419 times more pay than blue-collar workers, compared to a ratio of 42 times

     B     that, on average, CEO’s now earn 419 times the pay of blue-collar workers, a ratio that compares to 42 times

     C     that, on average, CEO’s now earn 419 times the pay of blue-collar workers, as compared to 42 times their pay, the ratio

     D    CEO’s who now earn on average 419 times more pay than blue-collar workers, as compared to 42 times their pay, the ratio

     E     CEO’s now earning an average of 419 times the pay of blue-collar workers, compared to the ratio of 42 times

从网上查阅as的用法：as单独引导定语从句

as单独引导定语从句时，先行词可以是一个词，也可以是一个句子或短语。

此两处如果均是以上用法，那么as的先行词补齐分别是什么？

139题C的错误在哪里?

没辙了，老是发两遍。请NN多多指教！