老prep一道关于quantity和fraction的题，求助

rinalin1992

                       

Thecontinental United States receives an average of 30 inches ofprecipitation a year; transpiration from soil and from plantsreturns approximately 21 of the 30 inches to the atmosphere, whilethe balance of 9 inches contributes to the flow of streams andrivers.

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

(B)even though transpiration from soil and from plants returnsapproximately 21 of the 30 inches to the atmosphere, the remainder of9 inches contribute to the flowing

(C)although transpiration from soil andfrom plants return approximately 21 ofthe 30 inches to the atmosphere, the balance of9 inches contribute to theflowing

(D)with transpiration from soil and from plants to return approximately21 inches to the atmosphere, the rest of the 9 inches contributes tothe flow

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

d选项为什么不对？
还有9 inches到底算是单数还是复数呢？