The best evidence that storytelling helped the narrator build a bond with his grandchildren is:
C. For the remainder of my visit, and during subsequent visits, I told her, and when he was old enough, my grandson, of the world around us and how we hoped to, some day, live together on Planet Earth. (paragraph 2)
This quotation illustrates the ongoing interaction and connection the narrator established with his grandchildren through storytelling, emphasizing the importance of sharing stories to strengthen their bond.