What Is the Purpose of the Salt Bridge in a Voltaic

What is the purpose of the salt bridge in a voltaic cell?

A) to prevent any further migration of electrons through the wire
B) to allow for the build up of positively charged ions in one container and negatively charged ions in the other container
C) to allow the $\mathrm { Fe } ^ { 2 + }$ and the $\mathrm { Cu } ^ { 2 + }$ to flow freely between the two containers
D) to allow for a balance of charge between the two chambers