题目选项分析

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, which thereby reduces the rate they burn energy so that it is 25 percent lower than isolated birds.

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.