They all produce light. They all cause vibrations. They all convert heat to energy. They all need gravity to move.
I gave my students this multiple choice question: What do playing a guitar, banging a drum, and dropping a pebble in the water have in common?

Only one answer is correct among these 4 choices:
- They all produce light.
- They all cause vibrations.
- They all convert heat to energy.
- They all need gravity to move.

Could you tell me which one is correct?

They all cause vibrations.