There is no mention of either specific heats larger than water's or solid vs. other phases in the passage. So A and D can be eliminated. The second law says that the entropy of the universe always increases. This problem has nothing to do with entropy - only enthalpy and heat. So B must be correct. It's correct because it says specifically in the passage that this is a "fast and localized heating process" which creates sound waves that can then be recorded.
