Final answer:
Salt water is the best conductor of electricity due to the presence of ions, while pure water, dry cotton, and wood are insulators.
Explanation:
Salt water would be the best conductor of electricity among the options provided. In this case, the salt dissolves in water to form ions, which can carry an electric current. Pure water, dry cotton, and wood are insulators, meaning they do not conduct electricity due to the lack of free-moving ions.
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