请教大牛们一个PREP2012的新题

auspex

In order to conserve the energy and heat they need to spend the entire winter sitting motionless over incubating eggs, male emperor penguins huddle over the nests in groups, thereby reducing the rate at which they burn energy so that it is 25 percent lower than it would be for isolated birds.

A)thereby reducing the rate at which they burn energy so that it is 25 percent lower than it would be for
B)thereby reducing their rate of burning energy until it is 25 percent lower when compared with
C)and they thereby reduce by 25 percent the rate they burn energy, as compared to what it would be with
D)which thereby reduces by 25 percent their rate of burning energy, when comparing them to
E)which thereby reduces the rate they burn energy so that it is 25 percent lower than

答案选A。
我想问问A中reducing的逻辑主语是不是male emperor penguins而不是整个主句？然后A后面的so that部分则是这个分句的从句部分吧？谢谢！

tzhou7

你可以认为reducing的逻辑主语是male emperor penguins，这里reducing.....修饰动词huddle over（也就是修饰整句）做伴随结果状语；
so that部分理解应该是正确的。