Explanation please

And also why it is not D?

The author attacks the study by pointing out that the study was only conducted in one language, which misses the possibility that many children who are bilingual may engage in linguistic borrowings. This is a perfect match for e. B is wrong because the author doesn't point out an inconsistency, but attacks the study's methodology. D is wrong because the author doesn't suggest a different set of advantages from the traditional assumptions, and the study in question suggested a disadvantage not an advantage.