When you combine the intermediate chemical equations, which substance do you cancel out?

In an example equation where AB + CD = AD + CB  the intermediate step would break all of the bonds before reforming them to look something like
AB + CD = A + B + C + D
A + B+ C + D = AD + CB

So combining the intermediate steps you cancel out like terms for the intermediate compounds.  If you have a specific chemical reaction I could help more.

Okay well gravitational energy is matter forced by gravity making energy though the kinetic energy then the electric energy produces electricity from the kinetic energy and the kinetic energy gets its energy from the gravitational energy. was that the answer you wanted or something else?  

Ithink the answer is b.