Which action changes the identity of the substance referenced? Breaking an ice cube; running an electric current through copper; burning wood; melting gold.(I’m not sure what it means by substance referenced)

The correct answer is:   [a]:   the "stratosphere" .

Sorry im just trying to get answers like you are 

The internal energy of the system we can term it as total potential energy and kinetic energy. energy flows out of the surrounding from the system then we can say that the internal energy of the final state is lower than its initials. the sign of  δesystem is negative.δesystem = efinal - einitial=-ve  efinal  ∠einitial.

Where? we need more.