I am pretty sure the answer is C. Don't take childhood for granted. He feels like he did in his childhood, but he dismissed it when younger.
A quote from the paragraph says,"<span>He supposed that, if he had ever thought about that deep-running aquifer of energy as a kid (he could not recall that he ever had), he would have simply dismissed it as a fact of life, something that would always be there, like the color of his eyes . . . ."
That is why I think the answer is C. Don't take your childhood for granted. </span>
I believe the answer is second person because she refers to her as you which is a second person pronoun
