【英语时差8,16】马的腿为什么这么细？2

 Why horses have skinny legs? What’s the use of a skinny leg? The answer is Running. The skinniest lower legs belong to the fastest runners. Think of how a deer can move, as opposed to a tortoise. Why is that? It’s because when you run, or indeed walk, you are constantly swinging the bottom halves of your legs. For humans, one foot is stopped and essentially¹ resting on the ground while the other is moving twice as fast as your overall speed.

1 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。