Here's a problem to solve: A pan of soup is being heated on an electric stove. A metal spoon is used to occasionally stir the soup. Which of the following is an example of heat being transferred by convection?

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

- A: heating the pan
 
- B: heating the soup
 
- C: heating the spoon
 
- D: heating the stove burner
 