]The history of renewable energy suggests there is a steep learning curve, meaning that, as more is produced, costs fall rapidly because of economies of scale and learning by doing. The firms' green innovation is path- dependent: the more a firm does, the more it is likely to do in the future. The strongest evidence for this is the collapse in the price of solar energy, which became about 90% cheaper during the 2010s, repeatedly beating forecasts. Moving early and gradually gives economies more time to adjust, allowing them to reap the benefits of path- dependent green investment without much disruption. A late, more chaotic transition is costlier. Which one of the following statements best reflects the central idea of the passage?

The central idea of the passage revolves around the implications of the characteristics of green energy (steep learning curve, path-dependency) for the transition process. Option A is incorrect because while economies of scale are mentioned as a factor, they are not the central idea. The passage also highlights "learning by doing" and "path-dependency." Option B is incorrect because while path-dependent innovations are discussed in the context of green energy, the passage's main point is not about modern technological progress in general, but specifically about the strategic implications of green technology's characteristics for a smooth transition. Option C is incorrect because the passage discusses "economies" in general, not specifically "large economies," and does not argue that size is the primary determinant for adopting green technologies. Option D is correct because the passage explicitly concludes by stating the importance of timing: "Moving early and gradually gives economies more time to adjust, allowing them to reap the benefits of path-dependent green investment without much disruption. A late, more chaotic transition is costlier." This directly emphasizes the crucial role of timing in green technology development and adoption.