C) A modern newspaper is printed many more times than previous newspapers--and still is relatively cheap to buy.
The text says
"Johannes Gutenberg made the earliest printing press, as we know it today, around 1450. These presses used movable type to create many pages of news faster and more easily than any other process. "
So the answer to the question (What can the reader infer the author means when he says that newspapers were not truly modern until after the invention of movable type?) is
C.