Answer:
C
Explanation:
take a look at this line again
<em>performing breathtaking feats
</em>
<em>of aquatic acrobatics for the sheer joy of it.</em>
Does that sound like silly and foolish to you? It doesn't to me. That answer should never be considered. Not D
Where's the stubborn part? Do the dolphins sound stubborn? Not B either.
What about flexible and powerful? I think this is likely your second best answer. It would take power to get them out of the water and to be acrobatic you need to be flexible. I wouldn't pick this answer, but I understand those who would.
To me the answer if C. They sound like they are having a lot of fun. And they are treating what they are doing with a lot of glee and much joy. What the author says is that it is breathtaking. C is the only answer you could pick.