15. please help

Use the following information to answer the next question A group of students wanted to determine which of four different objects would experience an electrostatic force of repulsion from the negatively charged top of the Van de Graaff generator I - Neutral polystyrene ball II - Positively charged polystyrene ball Ill - Negatively charged polystyrene ball IV - North end of a bar magnet 15. Which of the objects selected by the students will experience a force of repulsion from the top of the generator? () Objects Ill and IV only () Objects ll and IV LI Object Ill only () Objects | and Ill