The argument that BEST supports what will happen is:
An object with a positive charge will move toward the negative plate.
This is because charged plates create an electric field between them. A positively charged object will experience a force due to this electric field that directs it toward the negatively charged plate (since opposite charges attract), causing the positively charged object to move toward the negative plate.
The other options either incorrectly suggest movement for neutrally charged objects or repeat the same statement, which does not provide a valid basis for the behavior in the electric field created by the charged plates.