How to give the spheres exactly equal but opposite charges?

a. Make sure spheres are not in contact with each other. Rub the glass bring the rod without touching near one of the spheres. Do the same with a piece of silk and another sphere. Remove the glass rod and the piece of silk.
b. Put the two metal spheres in contact with each other. Then rub the glass rod on the silk to charge the rod positively (hence to charge piece of silk negatively). Bring the rod near, but not touching, one of the spheres. Separate the spheres and remove the rod
c. Put the two metal spheres in contact with each other. Then rub the glass rod on the silk to charge the rod negatively (hence to charge piece of silk positively). Bring the rod near, but not touching, one of the spheres. Separate the spheres and remove the rod
d. None of the above.