One SC question[原创]

nansresume

[em27]Car owners who inflate their tires properly can substantially boost their vehicles'fuel efficiency, since the increase in car-road friction can waste up to five percent of car fuel by underflation.(a)
Because the underflation of tires can waste up to five percent of a car's fuel by increasing car-road friction, car owners can substantially boost their vehicles' fuel efficiency by properly inflating the tires.(b)
(from 新东方语法书 Section 16 No. 22 P126 )
I think both a and b is right, but the kiy is b. Why?

tongxun

刚才回答到一半死机了，再来！
A、B两选项都没有重大错误，但ETS让我们选的是最好的，也就是说在所有选项中都有可能存在错误，看哪个错误最少。
A与B相比：1）原因状语从句的引导词一般用because，而since 较少用。
          2）B的句子意思表达顺畅，层次清晰
          3）by。。。，by。。。多好！
          4）最重要的是：B选项将“boost”的原因完全表达出来了，而A没有，导致从句原因的描述无所侍从。

nansresume

Thanks.