大全94、95，及while的用法？

94、  Although she had signed a pledge of abstinence while being an adolescent, Frances Willard was 35 years old before she chose to become a temperance activist.

(A) while being an adolescent

(B) while in adolescence

(C) at the time of her being adolescent

(D) as being in adolescence

95、 Although some officials noted that using machines for farming in China costs more than traditional hand cultivation, the mechanization of farming in the village of Long Bow doubled the corn yield while the previous year’s costs were cut in half.

(A) mechanization of farming in the village of Long Bow doubled the corn yield while the previous year’s costs were cut in half

(B) mechanization of farming in the village of Long Bow doubled the corn yield while cutting costs to half those of the previous year

(C) mechanization of farming in the village of Long Bow doubled the corn yield as cost were cut to half of the previous year’s

(D) farming mechanization in the village of Long Bow doubled the corn yield as it cut in half the previous year’s costs

(E) farming mechanization in the village of Long Bow doubled the corn yield while costs were cut to half that of the previous year

94题答案是E ，为什么不能选B？

95题答案是B 。为什么不能选C? 如果把C选项改为  mechanization of farming in the village of Long Bow doubled the corn yield as cost were cut to half those of the previous year，是不是就对了呢？

while表示“当……时候”的意思时，它后面可以跟什么成份？这个词到底应该怎样用啊? 第95题B选项里 while cutting costs to half those of the previous year 是一个什么结构啊？

唉，我都快晕死了！请大牛们指教一下吧！

刚刚又仔细体会了一下95题B选项的含义，B里面的while是不是表示转折意思，而不是“当……时候”的意思？while后面分词短语cutting costs to……是不是表示伴随动作：在double the corn yield的同时把成本降低到去年的一半？

这个while从我上中学时起就特别烦人，现在还在烦人……唉！