The argument that BEST supports what will happen is:
An object with a positive charge will move toward the negative plate.
This statement correctly describes the behavior of charged objects in an electric field created by two charged plates. A positively charged object will experience an attractive force towards the negatively charged plate. Meanwhile, a negatively charged object would move toward the positive plate. A neutrally charged object would experience no net force and remain stationary. Therefore, the statement about the positively charged object moving toward the negative plate is the best choice among the given options.