PT1.S3.Q.21- Animal Speed and Body Weight

abbymajerus

On this question I initially answered correctly, but then during BR changed to the wrong answer. I am beginning to understand why C is correct, but I still feel like I am not even 100% sure what the stimulus itself is actually saying.

Here is the stimulus:

The energy an animal must expend to move uphill is proportional to its body weight, whereas the animal's energy output available to perform this task is proportional to its surface area. This is the reason that small animals, such as squirrels, can run up a tree trunk almost as fast as they can move on level ground, whereas large animals tend to slow down when they are moving uphill.

What's throwing me off is that I don't understand how "energy output available to perform this task" differs from "energy an animal must expend." I was also a little confused by the jump from talking about energy to speed (saying that this is why squirrels can run up a trunk at the same speed)- am I meant to interpret that as saying that it uses the same amount of energy? If so, is that in relation to energy output available or the amount that must be expended and how would I know that?

Thanks for any help in advance!