Explanation: Buddhism spread out of India by means of merchants trading between India and its neighbors. Eliminate any answer choices that do not match this. Choice (A) helped the decline of Buddhism in India, so eliminate (A). Choice (B) is too limited, as the royal edicts supported India, not Buddhism specifically; get rid of (B). Choice (C) happened after 600 (C) E., so eliminate it, as it does not work chronologically. Choice (D) is correct; strong trade routes linking south, central, and east Asia helped spread Buddhist influence as shown on the map.