Here's a problem to solve: When a button is pushed on a battery-operated clock, the time display is illuminated. What process has taken place?

Among the 4 following options, which is the correct answer?

- A: Pressure has been converted to light.
 
- B: Force has been converted to light.
 
- C: Closing an electric circuit has produced light.
 
- D: Opening an electric circuit has produced light.
 