Here's a problem to solve: Students are investigating how a doorbell works. Which is most likely an observation made during the investigation?

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

- A: All doorbells make pretty sounds.
 
- B: A battery is the best power source for a doorbell.
 
- C: Most people prefer to use a doorbell over knocking.
 
- D: The doorbell uses a piece of wire wrapped around a magnet.
 