Sentence Correction

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

The first split is in how to introduce the modifier: "reducing" or "which reduces". Modifiers introduced with "-ing" modify the action in the previous clause, while modifiers introduced with a relative pronoun (which, when, who...) modify the noun phrase just before the comma. In this case, since we want to modify the whole action ("penguins huddle in groups") rather than just "groups", modifiers beginning with "which" are not appropriate.

Also at issue is how to compare the rate at which huddled penguins burn energy to the rate at which isolated birds would burn the energy. The full solution below is taken from the GMATFix App.



-Patrick