[求助]OG 第 31题。前面有人问过，但没人解释清楚。

fightbear

以下是引用lcy19812000在2009-1-18 20:39:00的发言：

大全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（B）

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

可见，while表比较不能省略的理论是错误的。

我想关键的还是be+adj.和be+prep.结构就不能省吧。

这个例子while引导时间状语，lz的题while表示转折。while+时间状语省略是ets里的常态。