I think D is correct because if we look to the end of the 4th paragraph, it states: "cold, empty
space—not an obviously favorable starting point for the onset of inflation." This implies that cold, empty space isn't an obviously apparent prior condition to the Big Bang and so can be considered as "puzzling." The next paragraph then introduces recent research to explain how this "puzzling" state could have led to the Big Bang. The research about energy fluctuations is something that Carroll and Chen take into account and is thus "resolved" by their theory, not an implication of it.
