This is anti-supported by the passage. Mphahlele isn’t concerned with making sharp distinctions between fiction and autobiography.

This is such a tempting answer, because the author’s response to critics who don’t like Mphahlele’s blurring of literary categories is to say that these critics “inevitably miss the fact that Mphahlele manipulates different prose forms purely in service of the social message he advances.”

But this quote doesn’t mean the author thinks the critics find Mphahlele’s social message irrelevant. The point is that the critics are assessing Mphahlele’s work on a metric that Mphahlele doesn’t care about. The critics are either not aware of Mphahlele’s message, or don’t give it enough weight in their critical assessments of his work. If the critics knew what Mphahlele was trying to do, then maybe they would change their views about his work. So, although the author might think Mphahlele’s goal of conveying a social message should be more relevant to the critics than it is, that doesn’t mean it lacks all relevance to them.

There’s no evidence that critics’ concern with categorization isn’t related to their judgments about the quality of works. Maybe if a work doesn’t fit a category well, the critics view the work as worse. The critics mentioned in the passage might view Mphahlele’s works as worse because they don’t adhere to sharp distinctions between autobiography and fiction.

This is strongly supported by the end of the second paragraph: “but critics often balk at [Mphahlele’s vision of the future] because Mphahlele provides no road maps for bringing such a future about.” If one of the reasons the critics don’t like Mphahlele’s vision is the lack of a road map, that suggests if Mphahlele did provide a road map, the critics might like his vision more.

If you don’t like this answer, it’s probably because you’re holding the correct answer to too high of a standard. (D) isn’t a “must be true” answer. But when we’re told the cause of a particular effect, that provides some evidence that if the cause weren’t present, there’s a possibility the effect might not be present.

The passage suggests that some critics might hold this opinion. But that’s not the same as strongly suggesting that this opinion is true.