Question: Alex looked at an electric toothbrush that had a plug with three metal prongs. Why are these prongs made out of metal?

  Options: 
 A. Metal doesn't get hot and melt when you plug it into the outlet.
 B. Metal is strong and is less likely to break when you plug it into the outlet.
 C. Metal is an insulator and prevents shocks when you plug it into the outlet.
 D. Metal is a conductor and completes a circuit when you plug it into the outlet.
Answer: D