Solder is a silver metal used to hold pipes together. When the solder is heated, it melts and acts as a type of metal "glue." Mrs. Hanley heats a piece of solder until it melts between two pipes. What best identifies the point at which a physical change first takes place? A)when the solder melts

B)when the solder cools down

C)when the solder is a soft metal

D)when the solder becomes solid again