Which One of the Following Is a Chemical Change

Which one of the following is a chemical change?

A) When blood is mixed with 3% hydrogen peroxide solution, it changes color.
B) When water is boiled, it forms steam.
C) When a solid stick of butter is heated, it becomes a liquid.
D) When blue paint is mixed with yellow paint, a green colored paint is obtained.
E) When a bar of gold metal is pounded with a hammer, it flattens out.