OG详解-OG5 文法 Q13

Choice C is the best answer. The sentence specifies how the salt in a freeze-thaw battery enables energy storage, explaining that energy stops flowing and can be stored when the salt solidifies at room temperature.
Choice A is incorrect. The sentence explains some properties of molten salt; it doesn’t specify how that salt enables energy storage. Choice B is incorrect. The sentence indicates how the energy in a freeze-thaw battery can be released; it doesn’t specify how the salt in the battery enables energy storage. Choice D is incorrect. The sentence specifies how much charge the freeze-thaw battery retains when storing energy; it doesn’t specify how the salt in the battery enables energy storage.