Here's a problem to solve: A student is investigating the temperature at which evaporation takes place. Which statement best shows that evaporation has taken place?

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

- A: Rain falls from the sky.
 
- B: The sky is clear of clouds.
 
- C: Water droplets appear on the grass.
 
- D: Water droplets disappear from the grass.
 