The answer can be found in lines 45-50, pinsyuanwu, quoted here:
Here her determination to leave areas of ambiguity in the solution of the crime and to distribute guilt among the murderer, victim, and bystanders points to a conscious rebellion against the traditional neatness of detective fiction.
In these lines, the author is indicating that the traditional detective novel does not have these characteristics of James' latest book. It does not have ambiguity in the solution, and guilt is not distributed. James is said to be rebelling against those traditions. That pretty strongly suggests that in a traditional detective novel, the solution to the crime should be clear, and the murderer should be the only party who is seen as guilty. That's the "straightforward culpability" in answer D!
The author seems to mostly like James' work, and thinks it's time for her to try something outside her usual genre, but he still has a clear sense of what that genre usually requires.
Adam M. Tyson
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