PREP 46

The continental United States receives an average of 30 inches of precipitation a year; transpiration from soil and from plants returns approximately 21 of the 30 inches to the atmosphere, while the balance of 9 inches contributes to the flow of streams and rivers.

(A) transpiration from soil and from plants returns approximately 21 of the 30 inches to the atmosphere, while the balance of 9 inches contributes to the flow

(B) even though transpiration from soil and from plants returns approximately 21 of the 30 inches to the atmosphere, the remainder of 9 inches contribute to the flowing

(C) although transpiration from soil and from plants return approximately 21 of the 30 inches to the atmosphere, the balance of 9 inches contribute to the flowing

(D) with transpiration from soil and from plants to return approximately 21 inches to the atmosphere, the rest of the 9 inches contributes to the flow

(E) as transpiration from soil and from plants return approximately 21 of the 30 inches to the atmosphere, the rest of the 9 inches contribute to the flow

怎么选A呢？C不行吗？

我觉得“transpotation.......”即整个划线部分在语法上是一个完整分句，但在意思上是仍在对precipiration部分进行补充说明，其中while引导的时间状语从句相当于at the same time

而although....表示“尽管21of30......,9......”在原文无明显问题时，改变原句的逻辑（and--but）和主从关系

^_^不知道你认为怎么样的呢