Pressure has been converted to light. Force has been converted to light. Closing an electric circuit has produced light. Opening an electric circuit has produced light.
I gave my students this multiple choice question: When a button is pushed on a battery-operated clock, the time display is illuminated. What process has taken place?

Only one answer is correct among these 4 choices:
- Pressure has been converted to light.
- Force has been converted to light.
- Closing an electric circuit has produced light.
- Opening an electric circuit has produced light.

Could you tell me which one is correct?

Closing an electric circuit has produced light.