Choice A is the best answer. The first paragraph of the passage makes clear that salt exhibits elasticity ("stretching like taffy") in the nanoworld, and the eighth paragraph explains that salt possesses some degree of elasticity in the macroworld as well: "Huge underground deposits of salt can bend like plastic, but water is believed to play a role at these scales." Thus flexibility describes the relationship between salt's behavior in both the nanoworld and the macroworld.
Choice B is incorrect because the third paragraph explains that "scientists don't expect" salt's flexibility in the nanoworld, not that they do expect it; moreover, there is no indication that salt's flexibility in the macroworld is surprising. Choice C is incorrect because the passage doesn't make clear whether nanowires were first observed in the nanoworld or the macroworld. Choice D is incorrect because the passage does not examine the interaction of salt and water in the nanoworld or suggest that such interaction causes salt to have properties that are different from those it possesses in the macroworld.