B. To reflect the realities of life in his writings.
Explanation:
Mark Twain wrote about lower-class citizens in his satires to show people who read his satires, the reality of which lower-class people had to live in, with it being hard and cruel.
The answer would be D. to give readers a sense of what his life was like as a child.
As an author, sometimes it’s their goal to enlighten a reader and make the reader more open to all aspects in the book. Sometimes that is done by giving some background information to help.