Based on these lines from"the gorgon's head" by nathaniel hawthorne is an imperative sentence is: b. "be careful that they do not see you before you see them".
the "imperative" sentence is a command, so i think it's the answer b.
hope this help
If a bar of copper is brought near a magnet, the copper bar will be repelled by the magnet (B). Copper itself is not magnetic, but it sets up electric currents when a magnet is brought close to a bar of copper. These electric eddy currents push the magnet away from the copper bar. Magnetism and electricity are related and the interaction between the copper and a magnet is used in power plants to generate the electricity that we use every day.