In the first law of thermodynamics, angle e = q - w, what does angle e stand for? a. the heat added to the system b. the internal energy of the system c. the work done by the piston d. the change in the internal energy of the system

I guess my answer got deleted for some reason so here it is again, Angle E stands for the change in the internal energy(E standing for energy) of the system so D.
In whole this equation can be written down as, the change in the internal energy of the closed system, equal too the heat added to the system, minus the work done by the system.

Outermost (valence) electrons