Final answer:
Option 3: C. As the swing goes from position c to position b, the potential energy decreases and kinetic energy increases due to the conversion of energy types as the swing descends.
Step-by-step explanation:
When the swing moves from position c back to position b, the potential energy of the student decreases, and the kinetic energy of the student increases. This is because as the swing descends from its highest point (c) where it has the maximum potential energy, the swing converts this potential energy into kinetic energy as it gains speed towards the middle position (b). Therefore, the correct answer is Option 3: C. Potential energy of the student decreases and the kinetic energy of the student increases.