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第1段
1 .<-NARRATOR:-> Listen to part of a lecture in a biology class.
请听生物课上的部分内容。
第2段
1 .<-FEMALE PROFESSOR:-> Many animals live underground, in the soil.
很多动物都生活在地下，在土里。
2 .Not just little animals like worms,
不只是像虫子这样的小动物，
3 .but also bigger animals, like mammals.
还有像哺乳动物这样的大一些的动物。
4 .Living underground has advantages. It protects animals from above-ground predators.
生活在地下有其优势，能够保护动物不受地上捕食者的侵害。
5 .However, the underground environment also presents challenges.
可是，地下环境同样也存在着挑战。
6 .And animals that live underground have developed physical adaptations to deal with them.
所以生活在地下的动物进化出了能够对付这些挑战的身体能力。
7 .One challenge is,
其中一个挑战，
8 .well, simply how to move underground, through the dirt.
只不过就是如何穿过泥土在地下行动。
9 .Another challenge for the animal is to protect vulnerable parts of its body from the environment that it's moving through.
动物面临的另一个挑战是保护身体脆弱的部位不受周围环境的影响。
第3段
1 .Now, moving through soil is not like moving through air or water,
穿过泥土和在空中或水中行动完全是两回事，
2 .because soil, earth, is thick and dense.
因为泥土，土壤，又厚又密。
3 .So animals that live underground have evolved physical features that help them move through dirt efficiently.
因此，生活在地下的动物进化出了能够帮助它们有效地穿过泥土的身体特征。
4 .For example, the mole, a small, furry mammal,
比如鼹鼠，一种小小的，毛茸茸的哺乳动物，
5 .has really wide, super-strong front feet with big claws.
它长着有一对大爪子的前脚，它的前脚很宽，超级强壮。
6 .The mole's feet act like, uh,
鼹鼠的前脚就像...
7 .like shovels-so it can dig through the dirt.
像铲子一样，所以它可以在土里挖通道路。
8 .The claws cut into the dirt, loosen it up, and then, once the dirt is loosened up,
鼹鼠在土里前进的时候，会把爪子插进土里，把土弄松，一旦土松了，
9 .the broad feet throw the dirt behind the mole as it moves forward.
鼹鼠向前移动时，宽阔的双脚把泥土抛在身后。
10 .These shovel-like front feet allow a mole to dig its way through the dirt astonishingly quickly.
这些铲子一样的前脚使得鼹鼠可以很快地在土中挖出道路前进，速度快得令人震惊。
第4段
1 .But even for an animal that can move efficiently through the dirt,
但是即使对那些能够在土中迅速移动的动物来说，
2 .living underground can still be problematic,
生活在地下也还是充满问题的。
3 .because it's easy for particles to get caught in sensitive parts of the animal's body,
因为泥土颗粒很容易会掉进动物身体的敏感部位，
4 .like, for mammals, in their eyes.
比如对于哺乳动物来说，会掉进它们的眼睛里。
5 .So underground animals have developed adaptations to prevent this.
所以生活在地下的动物进化出了能够预防这种情况的能力。
6 .Again, let's take the example of the mole.
我们再次以鼹鼠为例。
7 .To begin with, moles have tiny eyes.
首先，鼹鼠们的眼睛非常小，
8 .And these eyes are covered with a thin skin,
而且眼睛上覆盖着一层很薄的皮肤，
9 .a protective membrane that's actually got hair on it.
这是一种实际上长着毛的保护性薄膜。
10 .These hairs protect the mole's eyes from dirt particles.
这些毛发能够防止泥土颗粒进入鼹鼠的眼睛。
11 .So as the mole goes digging through the dirt with its head pushed forward,
所以当鼹鼠头朝前在土里挖通道路的时候，
12 .the dirt particles come into contact with the hairy membrane covering the mole's tiny eyes,
这些泥土颗粒接触到的就是覆盖着它的小眼睛的毛茸茸的薄膜。
13 .and the particles just slide by,
接着这些颗粒就会顺势滑落，
14 .don't get caught in the mole's eyes.
不会掉进鼹鼠的眼睛里。
15 .So the eyes, the mole's sensitive parts, are protected.
于是鼹鼠的眼睛，它的敏感部位，就得到了保护。