Answer:
D. Cast iron
Explanation:
Sound requires a medium to travel. More specifically, it relies on medium particles to vibrate, touching each other and propagating the sound through the medium. Knowing that then, it should follow that solids are the best conductors of sound because the particles in a solid are packed tightly together which vibrations travel faster unlike in a gas where it takes a lot for particles to touch since they are so far apart from each other.
So cast iron is the correct answer.
