Final answer:
Energy is added to the system when two particles with like charges are brought closer together, as work must be done against the repelling electrostatic forces.
Step-by-step explanation:
When two particles with like charges become closer together, energy is added to the system, making the correct answer (a) Energy is added. According to principles of electrostatics, like charges repel each other. When these particles are brought closer, work must be done against the electrostatic force that is trying to push them apart. This work results in an increase in the potential energy of the system, which reflects the energy added to the two-charge system. Therefore, if you have two positively charged or two negatively charged particles, moving them closer will require you to do positive work, and the internal energy of the system will increase.