To me the answer is B because that one doesn't really sound right compared to the other answers.
I would have to say that the best way to revise sentence four is by changing "aren't" and "they're" to "are not" and "they are."
"Argue" works better than "fight."
Deleting the entire sentence would remove the transition into cost efficiency of the tablets.
And moving the sentence to the end would place the transition to cost efficiency in the wrong place.
