How do you know the writer used a point-by-point comparison strategy in the passage?

a.
The writer combines information about both kinds of books in each paragraph.

b.
The writer discusses e-books for several paragraphs and then discusses print books until the end.

c.
The writer covers all the information about e-books and then print books.

d.
The writer moves between the two kinds of books, back and forth, throughout the passage.