An artist heats a solid iron rod and bends it into a new shape. What happens to the iron atoms as the temperature of the solid iron rod increases?

A-The iron atoms move more slowly after they are heated.
B-The iron atoms move more quickly after they are heated.
C-The iron atoms were not moving before they were heated, and they are not moving after being heated.
D-The iron atoms were moving before they were heated, and they continue to move at the same speed after being heated.