OE


As the second half of the sentence informs you, light has some unusual - and confusing - properties. The missing word could mean something as simple as interested, but it is possible that even these thinkers have found the nature of light perplexing, so we could also be looking for a word meaning confused. In either case, placated does not make sense, because even if scientists could be appeased by questions about light, why would they need to be appeased in the first place? Fettered is too strong a word; it means confined or restrained. To implicate means to show to be involved in or to connect or relate to intimately - eliminate it. Finally, enervated means weakened or deprived of strength; clearly scientists cannot have been too weakened by these questions, or they would never have made any progress. Eliminate it. The best answer is confounded (bewildered).