The correct response is:
The electrons will move through the can first and then spread to the styrofoam cup. This is because the metal can is a conductor.
Explanation: When the negatively charged balloon is brought close to the styrofoam cup, which is insulating but has a metal can on top, the negatively charged electrons from the balloon will be attracted to the positive charge in the metal can. Since the metal can is a conductor, the electrons can move through it easily and redistribute themselves, affecting the styrofoam cup as well.