Explanation
Correct answer: A.
Choice A is the best answer. The text starts by stating what moral philosophy is concerned with and naming two examples of works in the field. Then it describes a shortcoming of some works in that field (they say how but not why), and finally it states that other works try to avoid that shortcoming (by including both how and why to live a morally good life).
Why the other choices are wrong
Choice B
Choice B is incorrect. This is too extreme. The text never mentions whether the two works are popular or not, and it never argues that these works don’t serve their intended purpose of describing how to live a morally good life. Rather, the text claims that works of moral philosophy that don’t include both how and why to be moral are not useful to readers who don’t already want to be moral.
Choice C
Choice C is incorrect. This isn’t the overall structure. The text never discusses the history of moral philosophy at all, and it doesn’t propose any topic for further research.
Choice D
Choice D is incorrect. This isn’t the overall structure. The text never discusses which of the two works is more widely read.