Here's a problem to solve: As part of a study, a scientist observed a number of different molecular changes in matter. Which of the following observations provides evidence of a physical change?

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

- A: using heat to burn a log in a fireplace
 
- B: using light to produce sugar in plants
 
- C: a cake that was baked from many ingredients
 
- D: a bottle that was broken into many small pieces
 