Final answer:
When two charged spheres with opposite charges are brought close to each other, they swing towards each other due to the attractive electrostatic force.
Step-by-step explanation:
The correct answer is a. swing towards each other due to the attractive electrostatic force between them. When two charged spheres with opposite charges are brought close to each other, they experience an attractive force due to the electrostatic interaction between the charges. This force causes the spheres to swing towards each other. For example, if one sphere has a positive charge and the other has a negative charge, they will attract each other and swing towards each other.