Hi, I think there are two issues with D. First, the passage was heavily focused on why and how leading questions are bad, and D fails to touch on this, while B does.
Second, the idea that the effects of leading questions are virtually impossible to mitigate goes beyond what the passage actually said. While I came away with the impression that it's quite hard to minimize their impact, I don't really see any support for the idea that it's not possible to do.
